When a new appointment or event is created in the Xiaomi smartphone's Calendar app, the device automatically selects the default reminder time. If we don't want to have to change it each time, we can set it in the preferences. The following options are available:

Android 10 | MIUI 12.0
Step 1:  Open the  Calendar app
Step 2:  Open the  menu
Step 3:  Open the  Settings
Step 4:  Tap on  Default reminder time
Step 5:  Set the  Default reminder time
  1. Open the Calendar app
  2. Open the menu
  3. Open the Settings
  4. Tap on Default reminder time
  5. Set the Default reminder time

Xiaomi Instructions