I expect Apple to figure out how to provide apps with such a timer in a way that also prevents them from having access to the system uptime.

If there's a random offset applied, how would they have access to the actual system uptime?

I don’t know, like I said, I expect Apple to figure that out. Their engineers get paid to figure out such problems, not me!

My original response in this thread was to a comment that said, "I'm not comfortable with the offset either".

I expect privacy theater; I err towards having opinions that enforce privacy - i.e. a time that's guaranteed to be x seconds since the app first started after system boot can be used to diminish privacy

Why would you expect privacy theater, though. Apple genuinely tries to frustrate this kind of snooping from (third-party) apps, so if they choose to obfuscate the timer in the first place, I don't see what the point is for them to make it a security theater. The obvious and trivial implementation for this is adding a random number, and that's what any minimally competent dev will do unless specifically told otherwise. So, why would they be told otherwise?