Eirikr70 I meant another point : you can expect a call and and not know that you have been switched off the grid.
I think the intention of the auto-reboot timer is for it to be set to an interval long enough that it reboots only if you have been involuntarily separated from your phone. So if you, personally, would plausibly have your phone safely with you for 18 hours without unlocking it, you might choose an auto-reboot interval longer than 18 hours.