Samsung
Change Auto-lock Time auf Samsung
Samsung phones running One UI lock the screen based on a short timer that starts as soon as the display turns off. If that timer is set to a very short value, the phone can feel like it locks instantly, even if you only glanced away for a second.
The setting responsible for this is Auto lock when screen turns off, found inside the secure lock settings. It only appears once a Pattern, PIN, Password or biometric method is active, since it works together with your screen lock.
To change it, open Settings ➔ Lock screen ➔ Secure lock settings. Confirm your current Pattern, PIN or Password when asked. Then tap Auto lock when screen turns off and choose an option, ranging from immediate locking to a delay of several seconds.
A longer delay is useful if you frequently glance at your phone and turn the screen back on within a few seconds. A very short or immediate setting is the safer choice on shared or public devices, since it removes the window where the phone stays unlocked after the screen goes dark.
This setting only affects locking speed. It does not change how long the screen stays on before turning off, which is handled separately under display timeout.