If you don't operate anything after waking up your cover screen, it enters Sleep mode with screen turned off according to automatic sleep time you set up. The default automatic sleep time is 3 seconds. However, if you go on operating your device, it goes to sleep according to the time for Automatic sleep that you set up. This battery-optimized default ensures battery power is not wasted on inactivity.
To setup your favorite Automatic sleep time, follow below steps:
Launch Settings > ASUS Cover > Automatic sleep.
Select your preferred Automatic sleep time from the given list.
Note: If you use a non-official cover accessory, some functions may not work properly. Check out the official ASUS website to see the latest ASUS official cover accessory.