diff --git a/homeassistant/components/mqtt/datetime.py b/homeassistant/components/mqtt/datetime.py
index 271fcb07a13f5..2e6cb9f04b55c 100644
--- a/homeassistant/components/mqtt/datetime.py
+++ b/homeassistant/components/mqtt/datetime.py
@@ -104,20 +104,7 @@ def config_schema() -> VolSchemaType:
 
     def _setup_from_config(self, config: ConfigType) -> None:
         """(Re)Setup the entity."""
-        self._zone_info = None
-
-        async def async_set_zone_info(timezone: str) -> None:
-            self._zone_info = await async_get_time_zone(timezone)
-            if self._zone_info:
-                return
-            _LOGGER.warning(
-                "Ignoring invalid timezone identifier for entity %s, got '%s'",
-                self.entity_id,
-                timezone,
-            )
-
-        if timezone := config.get(CONF_TIMEZONE):
-            self.hass.async_create_task(async_set_zone_info(timezone))
+        self._timezone_config = config.get(CONF_TIMEZONE)
 
         self._command_template = MqttCommandTemplate(
             config.get(CONF_COMMAND_TEMPLATE),
@@ -131,6 +118,18 @@ async def async_set_zone_info(timezone: str) -> None:
         self._optimistic = optimistic or config.get(CONF_STATE_TOPIC) is None
         self._attr_assumed_state = bool(self._optimistic)
 
+    async def _async_finish_update_config(self) -> None:
+        """Called after added to hass and after discovery update."""
+        self._zone_info = None
+        if timezone := self._config.get(CONF_TIMEZONE):
+            self._zone_info = await async_get_time_zone(timezone)
+            if not self._zone_info:
+                _LOGGER.warning(
+                    "Ignoring invalid timezone identifier for entity %s, got '%s'",
+                    self.entity_id,
+                    timezone,
+                )
+
     @callback
     def _handle_state_message_received(self, msg: ReceiveMessage) -> None:
         """Handle receiving state message via MQTT."""
diff --git a/homeassistant/components/mqtt/entity.py b/homeassistant/components/mqtt/entity.py
index 0b1b80fc4507a..8a26e454e9f83 100644
--- a/homeassistant/components/mqtt/entity.py
+++ b/homeassistant/components/mqtt/entity.py
@@ -1476,6 +1476,7 @@ async def async_added_to_hass(self) -> None:
             self._update_registry_entity_id = None
 
         await super().async_added_to_hass()
+        await self._async_finish_update_config()
         self._subscriptions = {}
         self._prepare_subscribe_topics()
         if self._subscriptions:
@@ -1493,6 +1494,12 @@ async def mqtt_async_added_to_hass(self) -> None:
         To be extended by subclasses.
         """
 
+    async def _async_finish_update_config(self) -> None:
+        """Called after added to hass and after discovery update.
+
+        To be extended by subclasses.
+        """
+
     async def discovery_update(self, discovery_payload: MQTTDiscoveryPayload) -> None:
         """Handle updated discovery message."""
         try:
@@ -1503,6 +1510,7 @@ async def discovery_update(self, discovery_payload: MQTTDiscoveryPayload) -> Non
         self._config = config
         self._setup_from_config(self._config)
         self._setup_common_attributes_from_config(self._config)
+        await self._async_finish_update_config()
 
         # Prepare MQTT subscriptions
         self.attributes_prepare_discovery_update(config)