Samsung
Set App Timers auf Samsung
App Timers sit inside Samsung's Digital Wellbeing tools and work per app, not per device. Once the daily allowance you set is used up, the app closes itself and stays greyed out until the clock passes midnight, when the counter resets.
This is different from Focus mode or a full screen-time schedule: only the apps you pick individually get a timer, everything else on the phone stays usable as normal. It fits well when one specific app, a game, a social feed, or a video app, eats more time than intended, but it will not help if the real issue is overall phone usage spread across many apps.
To set it up: Tap on Settings ➔ Tap on Digital Wellbeing and parental controls ➔ Tap on App timers ➔ Tap on Timer ➔ Set the Timer and tap Done.
One limitation worth knowing before you rely on this: apps inside Secure Folder and dual-app clones are not affected by the timer, since the system treats them as separate copies. If you need to restrict those too, manage them separately or move them out of Secure Folder first.