Open the "Settings" of Xiaomi phone, and click "Lock screen"-"password and fingerprint" under the system and device categories; find the "Auto Lock screen" setting item under the lock screen category; MIUI provides 7 settings from 15 seconds to never, and select the screen time you need to click to complete the settings.
The specific settings are as follows:

Step 1. Open the phone's [Settings], drop down the settings menu, find the [Lock screen, password and fingerprint] setting option under the system and device categories, and click to enter;

Step 2. Find the [Auto Lock screen] setting item under the lock screen category, and click to enter;

Step 3. MIUI provides 7 settings from 15 seconds to never, select the screen time you want to highlight according to your needs, and click to complete the setting. 

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