This function is designed to prevent you from wasting your working time on updates, so it will be automatically updated at night.
Setting method:
realme UI 3.0 & above versions: Settings > About device, click Up to date at the top > click 
in the upper right corner > Auto update > Turn on / off Auto-update overnight
realme UI 1.0 & 2.0: Settings > Software update > Click the Settings button in the upper right corner > Turn on / off Auto-update overnight
realme UI T & U Edition: Settings > System > Software update > Click the Settings button in the upper right corner > Auto-update overnight
realme UI R & Go & S Edition: not support. You can manually update system. Settings > System update
Note: After turning on Auto-update overnight, the latest software functions and security patches will be updated for you as soon as possible, and will not consume data. Auto-update overnight is processed from 2:00 to 5:00 at night.