Leave iPhone unlocked for a few seconds after closing
In the Face ID &amp; Passcode settings, you could set it to lock after 1, 5, 15 minutes or 1, 4 hours after the screen goes black. 

Additionally, you should be able to create an alternative appearance for Face ID to include your Face when you have your mask on? I've set 2 appearances, one with glasses and one without. You may have to reset the Face ID to set up additional appearances though. 

Hope this helps.

Edit

Here's the screenshots in the Face ID &amp; Passcode settings where you can set the time it locks after the screen goes black.