diff --git a/superset/db_engine_specs/postgres.py b/superset/db_engine_specs/postgres.py
index c5ffc79ee7100..4b8a731d31fa4 100644
--- a/superset/db_engine_specs/postgres.py
+++ b/superset/db_engine_specs/postgres.py
@@ -84,14 +84,14 @@ class PostgresBaseEngineSpec(BaseEngineSpec):
 
     _time_grain_expressions = {
         None: "{col}",
-        "PT1S": "DATE_TRUNC('second', {col})",
-        "PT1M": "DATE_TRUNC('minute', {col})",
-        "PT1H": "DATE_TRUNC('hour', {col})",
-        "P1D": "DATE_TRUNC('day', {col})",
-        "P1W": "DATE_TRUNC('week', {col})",
-        "P1M": "DATE_TRUNC('month', {col})",
-        "P3M": "DATE_TRUNC('quarter', {col})",
-        "P1Y": "DATE_TRUNC('year', {col})",
+        "PT1S": "DATE_TRUNC('second', {col})||':00'",
+        "PT1M": "DATE_TRUNC('minute', {col})||':00'",
+        "PT1H": "DATE_TRUNC('hour', {col})||':00'",
+        "P1D": "DATE_TRUNC('day', {col})||':00'",
+        "P1W": "DATE_TRUNC('week', {col})||':00'",
+        "P1M": "DATE_TRUNC('month', {col})||':00'",
+        "P3M": "DATE_TRUNC('quarter', {col})||':00'",
+        "P1Y": "DATE_TRUNC('year', {col})||':00'",
     }
 
     custom_errors: Dict[Pattern[str], Tuple[str, SupersetErrorType, Dict[str, Any]]] = {