Canardo_Sanchez the scenario would be to be forced to put your finger on the screen.
So the threat actor would take the device from you and force your finger on the screen, all without you being able to activate lockdown mode or turn off the device beforehand. The threat actor would need to take your device by surprise or in less than a minute, as that is the longest it would take you to deactivate the fingerprint sensor (blindly turn off your phone by holding the power button).
Canardo_Sanchez I guess I would have a timer between 30min and 1hour, but having as much options as the auto reboot feature would be great.
For the scenario described this would be way too long, right? It should ideally be 10-60 seconds, or at least a shorter time than your regular unlocking frequency so there's a fair chance the threat actor doesn't have the option to use your finger. But then a fingerprint setup becomes useless to you in the first place.
A lockdown timer would therefore either do the same as deactivating fingerprint unlock (if set to a low enough value) or it would be very unreliable and shouldn't be considered.
I suggest you find a reliable solution that works for your threat model. The available features might be enough (blind shutdown, lockdown shortcut, duress pin, 2FA pin, auto reboot). If they are not, the solution would lie elsewhere than in an automated lockdown timer...