Google Chromecast displays time and weather on your TV when it is idle. This is called Ambient mode. You can change the time zone and the time format from the Google Home app.

Change Time Zone and Time Format

To change time zone and time format of your Chromecast:

1. Open the Google Home app.
2. Tap and select your Chromecast device from the list of available devices.
3. Click the Gear icon on the top-right corner to access Device settings.
4. Scroll down to the Time section of Device settings.
5. Tap Time Zone and select the new time zone of your choice.
6. To change the time format, tap Time Format, and choose between 24-hour format and 12-hour format.