diff --git a/files/securedrop-client b/files/securedrop-client
index 1da697b0a..4951775ce 100755
--- a/files/securedrop-client
+++ b/files/securedrop-client
@@ -10,5 +10,13 @@ cd /opt/venvs/securedrop-client
 # Check if qubes-db exists (and we are running in qubes)
 if [ ! -f "/usr/bin/qubesdb-read" ]; then echo "Not running in Qubes, client not starting." && exit; fi
 
+# EXPERIMENTAL(#1547): Check for the SDEXTENDEDTIMEOUT_N service flag and export it as
+# SDEXTENDEDTIMEOUT=N.
+timeout_flag_value=$(qubesdb-list /qubes-service/SDEXTENDEDTIMEOUT_)
+if [ -n "$timeout_flag_value" ]; then
+	echo "SDEXTENDEDTIMEOUT=$timeout_flag_value"
+	export SDEXTENDEDTIMEOUT="$timeout_flag_value"
+fi
+
 # Now execute the actual client, only if running in an sd-app
 if [ "$(qubesdb-read /name)" = "sd-app" ]; then ./bin/sd-client; else echo "Not running in sd-app, client not starting."; fi
diff --git a/securedrop_client/api_jobs/sync.py b/securedrop_client/api_jobs/sync.py
index 3973a2c97..ee57140b1 100644
--- a/securedrop_client/api_jobs/sync.py
+++ b/securedrop_client/api_jobs/sync.py
@@ -1,4 +1,5 @@
 import logging
+import os
 from typing import Any, List, Optional
 
 from sdclientapi import API
@@ -18,6 +19,7 @@ class MetadataSyncJob(ApiJob):
     Update source metadata such that new download jobs can be added to the queue.
     """
 
+    DEFAULT_REQUEST_TIMEOUT = 60  # sec
     NUMBER_OF_TIMES_TO_RETRY_AN_API_CALL = 2
 
     def __init__(self, data_dir: str, app_state: Optional[state.State] = None) -> None:
@@ -40,7 +42,15 @@ def call_api(self, api_client: API, session: Session) -> Any:
         #
         # This timeout is used for 3 different requests: `get_sources`, `get_all_submissions`, and
         # `get_all_replies`
-        api_client.default_request_timeout = 60
+        api_client.default_request_timeout = int(
+            os.environ.get("SDEXTENDEDTIMEOUT", self.DEFAULT_REQUEST_TIMEOUT)
+        )
+        if api_client.default_request_timeout != self.DEFAULT_REQUEST_TIMEOUT:
+            logger.warn(
+                f"{self.__class__.__name__} will use "
+                f"default_request_timeout={api_client.default_request_timeout}"
+            )
+
         users = api_client.get_users()
         MetadataSyncJob._update_users(session, users)
         sources, submissions, replies = get_remote_data(api_client)
diff --git a/tests/api_jobs/test_sync.py b/tests/api_jobs/test_sync.py
index e8ec2342a..68f8ee6a1 100644
--- a/tests/api_jobs/test_sync.py
+++ b/tests/api_jobs/test_sync.py
@@ -14,6 +14,8 @@
 Submission = namedtuple("Submission", ["uuid", "source_uuid", "is_file", "is_downloaded"])
 File = namedtuple("File", ["is_downloaded"])
 
+TIMEOUT_OVERRIDE = 600  # sec
+
 
 class TestUpdateState(unittest.TestCase):
     def setUp(self):
@@ -37,6 +39,31 @@ def test_handles_missing_files_gracefully(self):
         assert self._state.file("9")
 
 
+def test_MetadataSyncJob_has_default_timeout(mocker, homedir, session, session_maker):
+    api_client = mocker.patch("securedrop_client.logic.sdclientapi.API")
+    remote_user = factory.RemoteUser()
+    api_client.get_users = mocker.MagicMock(return_value=[remote_user])
+
+    job = MetadataSyncJob(homedir)
+    job.call_api(api_client, session)
+    assert api_client.default_request_timeout == job.DEFAULT_REQUEST_TIMEOUT
+
+
+def test_MetadataSyncJob_takes_overriden_timeout(mocker, homedir, session, session_maker):
+    api_client = mocker.patch("securedrop_client.logic.sdclientapi.API")
+    remote_user = factory.RemoteUser()
+    api_client.get_users = mocker.MagicMock(return_value=[remote_user])
+
+    os.environ["SDEXTENDEDTIMEOUT"] = str(TIMEOUT_OVERRIDE)  # environment value must be string
+
+    job = MetadataSyncJob(homedir)
+    job.call_api(api_client, session)
+    assert api_client.default_request_timeout == TIMEOUT_OVERRIDE
+
+    # Don't pollute the environment for subsequent/out-of-order tests.
+    del os.environ["SDEXTENDEDTIMEOUT"]
+
+
 def test_MetadataSyncJob_creates_new_user(mocker, homedir, session, session_maker):
     api_client = mocker.patch("securedrop_client.logic.sdclientapi.API")
     remote_user = factory.RemoteUser()