I Just answer this in an other topic but I think it is better to create a new one only for this feature.
Unlock your device with the Fingerprint is very comfortable for the user. But a permanent activation can be dangerous that’s why I don´t use it.
Justification:
Suppose the timer is set to 1 hour. After you unlock your phone with the pin code, they can unlock your device with the fingerprint for 1 hour. If your device was stolen and the thief has the know-how to copy a fingerprint from your phone, he needs time to do it.
Let’s say he stole your phone and needs 30 minutes to go home and for example 1 hour to make a copy of a fingerprint from your phone. Doesn’t do him any good then either, because the scanner has long since been deactivated.