I think this is simply a matter of finding good defaults. In my opinion, the order of magnitude should be how many days without reception, not how many hours. A week sounds like a sane baseline for me, since that is more than ample time for most people to end up in a situation where you're connected again. Likewise you could reset the counter on a successful unlock. On the flip side, a week is not enough time to reasonably bruteforce anything if the time you have to wait before each retry goes up with every failure.