Though that's kind of a good question, GENERALLY speaking you should use "monotonic" timers for this sort of thing which don't have that problem. They're based

Though that's kind of a good question, GENERALLY speaking you should use "monotonic" timers for this sort of thing which don't have that problem. They're based on a system time which doesn't change. Of course, that's no guarantee.. this is done wrong in a lot of places all the time. But I would expect Apple to get this sort of basic thing right in their security code. Hopefully :)