I use Safe on my daughters phone running Android 7 but find that it does not block the use at the specified time. Instead it's approx 30mind late .
Since we had daylight saving time moving from GMT to BST it does not seem to work at all .
Sorry for my reply (I'm also only F-Secure user).
Just because there is not any replies yet.
Does your situation is about trouble state still?
If yes -> maybe it is an option to contact their direct Support Channels (chat or phone) for proper investigation:
With my own experience -> sounds that (at least, after first time installation and some network enabled/disabled states) time restrictions with normal design when it comes (not like delay with "thirty minutes"). But I did not try to re-check what will be if device clock is broken.
What about your second part and potential large impact -> I think that Support is most useful place (except official attention from F-Secure Teams under Community). Also, maybe it was known trouble and fixed already (?!).