diff --git a/.devcontainer/ui-lovelace.yaml b/.devcontainer/ui-lovelace.yaml
index 65520d9..fc179c6 100644
--- a/.devcontainer/ui-lovelace.yaml
+++ b/.devcontainer/ui-lovelace.yaml
@@ -13,7 +13,7 @@ views:
           - entity: sensor.random_0_1000
             name: Sensor 2
             type: area
-        hours_to_show: 0.20
+        graph_span: 15min
         cache: true
         layout: minimal
         header:
@@ -30,7 +30,7 @@ views:
           - entity: sensor.random_0_1000
             name: Ram Free
             type: area
-        hours_to_show: 0.20
+        graph_span: 15min
         cache: true
         layout: minimal
         header:
@@ -45,16 +45,16 @@ views:
           - entity: sensor.random_0_1000
             name: test2
             type: column
-        hours_to_show: 0.25
+        graph_span: 20min
         cache: true
       - type: custom:apexcharts-card
-        hours_to_show: 200
+        graph_span: 200h
         series:
           - entity: sensor.humidity
             curve: straight
 
       - type: custom:apexcharts-card
-        hours_to_show: 1
+        graph_span: 1h
         header:
           title: Test Aggregate
           show: true
@@ -98,7 +98,7 @@ views:
               func: first
 
       - type: custom:apexcharts-card
-        hours_to_show: 4
+        graph_span: 4h
         header:
           title: Test
         series:
@@ -119,7 +119,7 @@ views:
         graph: line
 
       - type: custom:apexcharts-card
-        hours_to_show: 6
+        graph_span: 6h
         header:
           show: false
         series:
diff --git a/README.md b/README.md
index 525584d..d09f3e3 100644
--- a/README.md
+++ b/README.md
@@ -92,7 +92,7 @@ The card stricly validates all the options available (but not for the `apex_conf
 | :white_check_mark: `type` | string | | v1.0.0 | `custom:apexcharts-card` |
 | :white_check_mark: `series` | array | | v1.0.0 | See [series](#series-options) |
 | `update_interval` | string | | NEXT_VERSION | By default the card updates on every state change. Setting this overrides the behaviour. Valid values are any time string, eg: `1h`, `12min`, `1d`, `1h25`, `10sec`, ... |
-| `hours_to_show` | number | `24` | v1.0.0 | The span of the graph in hours (Use `0.25` for 15min for eg.) |
+| `graph_span` | string | `24h` | NEXT_VERSION | The span of the graph as a time interval. Valid values are any time string, eg: `1h`, `12min`, `1d`, `1h25`, `10sec`, ... |
 | `show` | object | | v1.0.0 | See [show](#show-options) |
 | `cache` | boolean | `true` | v1.0.0 | Use in-browser data caching to reduce the load on Home Assistant's server |
 | `stacked` | boolean | `false` | v1.0.0 | Enable if you want the data to be stacked on the graph |
@@ -216,7 +216,7 @@ series:
 
 ```yaml
 type: custom:apexcharts-card
-hours_to_show: 6
+graph_span: 6h
 header:
   show: false
 series:
@@ -240,7 +240,7 @@ series:
 
 ```yaml
 type: custom:apexcharts-card
-hours_to_show: 1
+graph_span: 1h
 header:
   show: false
 series:
diff --git a/src/apex-layouts.ts b/src/apex-layouts.ts
index a3f3bc8..ab038cc 100644
--- a/src/apex-layouts.ts
+++ b/src/apex-layouts.ts
@@ -1,5 +1,6 @@
 import { HomeAssistant } from 'custom-card-helpers';
-import { moment } from './const';
+import parse from 'parse-duration';
+import { HOUR_24, moment } from './const';
 import { ChartCardConfig } from './types';
 import { computeName, computeUom, mergeDeep } from './utils';
 
@@ -45,7 +46,8 @@ export function getLayoutConfig(config: ChartCardConfig, hass: HomeAssistant | u
     tooltip: {
       x: {
         formatter:
-          config.hours_to_show < 24
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          parse(config.graph_span!)! < HOUR_24
             ? function (val) {
                 return moment(new Date(val)).format('HH:mm:ss');
               }
diff --git a/src/apexcharts-card.ts b/src/apexcharts-card.ts
index 14ebf88..30906a5 100644
--- a/src/apexcharts-card.ts
+++ b/src/apexcharts-card.ts
@@ -18,8 +18,9 @@ import {
   DEFAULT_DURATION,
   DEFAULT_FUNC,
   DEFAULT_GROUP_BY_FILL,
-  DEFAULT_HOURS_TO_SHOW,
+  DEFAULT_GRAPH_SPAN,
   DEFAULT_SERIE_TYPE,
+  HOUR_24,
 } from './const';
 import parse from 'parse-duration';
 
@@ -41,9 +42,13 @@ localForage
   .iterate((data, key) => {
     const value: EntityEntryCache = key.endsWith('-raw') ? data : decompress(data);
     const start = new Date();
-    start.setHours(start.getHours() - value.hours_to_show);
-    if (new Date(value.last_fetched) < start) {
+    if (value.span === undefined) {
       localForage.removeItem(key);
+    } else {
+      start.setTime(start.getTime() - value.span);
+      if (new Date(value.last_fetched) < start) {
+        localForage.removeItem(key);
+      }
     }
   })
   .catch((err) => {
@@ -73,6 +78,8 @@ class ChartsCard extends LitElement {
 
   private _colors?: string[];
 
+  private _graphSpan: number | null = HOUR_24;
+
   @property({ attribute: false }) private _lastState: (number | string | null)[] = [];
 
   public connectedCallback() {
@@ -148,10 +155,16 @@ class ChartsCard extends LitElement {
         throw new Error(`'update_interval: ${config.update_interval}' is not a valid interval of time`);
       }
     }
+    if (config.graph_span) {
+      this._graphSpan = parse(config.graph_span);
+      if (this._graphSpan === null) {
+        throw new Error(`'graph_span: ${config.update_interval}' is not a valid range of time`);
+      }
+    }
 
     this._config = mergeDeep(
       {
-        hours_to_show: DEFAULT_HOURS_TO_SHOW,
+        graph_span: DEFAULT_GRAPH_SPAN,
         cache: true,
         useCompress: false,
         show: { loading: true },
@@ -183,7 +196,7 @@ class ChartsCard extends LitElement {
             serie.entity,
             index,
             // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-            this._config!.hours_to_show,
+            this._graphSpan!,
             // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
             this._config!.cache,
             serie,
@@ -301,7 +314,9 @@ class ChartsCard extends LitElement {
     // const end = this.getEndDate();
     const end = new Date();
     const start = new Date(end);
-    start.setTime(start.getTime() - getMilli(config.hours_to_show));
+    // validated during Init
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    start.setTime(start.getTime() - this._graphSpan!);
 
     try {
       const promise = this._graphs.map((graph) => graph?._updateHistory(start, end));
diff --git a/src/const.ts b/src/const.ts
index d660039..15754d1 100644
--- a/src/const.ts
+++ b/src/const.ts
@@ -3,8 +3,9 @@ import { extendMoment } from 'moment-range';
 
 export const moment = extendMoment(Moment);
 export const ONE_HOUR = 1000 * 3600;
+export const HOUR_24 = ONE_HOUR * 24;
 
-export const DEFAULT_HOURS_TO_SHOW = 24;
+export const DEFAULT_GRAPH_SPAN = '24h';
 export const DEFAULT_SERIE_TYPE = 'line';
 export const DEFAULT_DURATION = '1h';
 export const DEFAULT_FUNC = 'raw';
diff --git a/src/graphEntry.ts b/src/graphEntry.ts
index be1ee1d..78e54c6 100644
--- a/src/graphEntry.ts
+++ b/src/graphEntry.ts
@@ -4,7 +4,7 @@ import { compress, decompress, log } from './utils';
 import localForage from 'localforage';
 import { HassEntity } from 'home-assistant-js-websocket';
 import { DateRange } from 'moment-range';
-import { DEFAULT_HOURS_TO_SHOW, moment } from './const';
+import { HOUR_24, moment } from './const';
 import parse from 'parse-duration';
 import SparkMD5 from 'spark-md5';
 
@@ -23,7 +23,9 @@ export default class GraphEntry {
 
   private _cache = true;
 
-  private _hoursToShow: number;
+  // private _hoursToShow: number;
+
+  private _graphSpan: number;
 
   private _useCompress = false;
 
@@ -43,7 +45,7 @@ export default class GraphEntry {
 
   private _md5Config: string;
 
-  constructor(entity: string, index: number, hoursToShow: number, cache: boolean, config: ChartCardSeriesConfig) {
+  constructor(entity: string, index: number, graphSpan: number, cache: boolean, config: ChartCardSeriesConfig) {
     const aggregateFuncMap = {
       avg: this._average,
       max: this._maximum,
@@ -58,19 +60,19 @@ export default class GraphEntry {
     this._cache = cache;
     this._entityID = entity;
     this._history = undefined;
-    this._hoursToShow = hoursToShow;
+    this._graphSpan = graphSpan;
     this._config = config;
     const now = new Date();
     const now2 = new Date(now);
     this._func = aggregateFuncMap[config.group_by.func];
-    now2.setHours(now2.getHours() - DEFAULT_HOURS_TO_SHOW);
+    now2.setTime(now2.getTime() - HOUR_24);
     this._timeRange = moment.range(now, now2);
     this._realEnd = new Date();
     this._realStart = new Date();
     // Valid because tested during init;
     // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
     this._groupByDurationMs = parse(this._config.group_by.duration)!;
-    this._md5Config = SparkMD5.hash(`${this._hoursToShow}${JSON.stringify(this._config)}`);
+    this._md5Config = SparkMD5.hash(`${this._graphSpan}${JSON.stringify(this._config)}`);
   }
 
   set hass(hass: HomeAssistant) {
@@ -129,7 +131,7 @@ export default class GraphEntry {
 
     let history = this._cache ? await this._getCache(this._entityID, this._useCompress) : undefined;
 
-    if (history && history.hours_to_show === this._hoursToShow) {
+    if (history && history.span === this._graphSpan) {
       const currDataIndex = history.data.findIndex((item) => item && new Date(item[0]).getTime() > start.getTime());
       if (currDataIndex !== -1) {
         // skip initial state when fetching recent/not-cached data
@@ -160,14 +162,14 @@ export default class GraphEntry {
         return [new Date(item.last_changed).getTime(), !Number.isNaN(stateParsed) ? stateParsed : null];
       });
       if (history?.data.length) {
-        history.hours_to_show = this._hoursToShow;
+        history.span = this._graphSpan;
         history.last_fetched = new Date();
         if (history.data.length !== 0) {
           history.data.push(...newStateHistory);
         }
       } else {
         history = {
-          hours_to_show: this._hoursToShow,
+          span: this._graphSpan,
           last_fetched: new Date(),
           data: newStateHistory,
         };
diff --git a/src/types-config-ti.ts b/src/types-config-ti.ts
index c9e57a9..acb7239 100644
--- a/src/types-config-ti.ts
+++ b/src/types-config-ti.ts
@@ -8,7 +8,7 @@ export const ChartCardExternalConfig = t.iface([], {
   "type": t.lit('custom:apexcharts-card'),
   "update_interval": t.opt("string"),
   "series": t.array("ChartCardSeriesExternalConfig"),
-  "hours_to_show": t.opt("number"),
+  "graph_span": t.opt("string"),
   "show": t.opt(t.iface([], {
     "loading": t.opt("boolean"),
   })),
diff --git a/src/types-config.ts b/src/types-config.ts
index 474d133..8ab57a1 100644
--- a/src/types-config.ts
+++ b/src/types-config.ts
@@ -2,7 +2,7 @@ export interface ChartCardExternalConfig {
   type: 'custom:apexcharts-card';
   update_interval?: string;
   series: ChartCardSeriesExternalConfig[];
-  hours_to_show?: number;
+  graph_span?: string;
   show?: {
     loading?: boolean;
   };
diff --git a/src/types.ts b/src/types.ts
index e0d6b5d..bbb1f59 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -3,7 +3,7 @@ import { ChartCardExternalConfig, ChartCardSeriesExternalConfig, GroupByFill, Gr
 
 export interface ChartCardConfig extends ChartCardExternalConfig {
   series: ChartCardSeriesConfig[];
-  hours_to_show: number;
+  graph_span: string;
   cache: boolean;
   useCompress: boolean;
   apex_config?: ApexOptions;
@@ -19,7 +19,7 @@ export interface ChartCardSeriesConfig extends ChartCardSeriesExternalConfig {
 }
 
 export interface EntityEntryCache {
-  hours_to_show: number;
+  span: number;
   last_fetched: Date;
   data: EntityCachePoints;
 }