I've never seen a CM interact with their board when scanning 5 min early or 15 min late. Anything outside of this window they've either denied entry or had to override. So I have no reason to think the 5 early/15 late isn't built into the system.
Some people have said they entered more than 5 min early and it automatically turned green, but I dont believe that. I'm guessing either their watch was slow, or they didn't look at the time. I accidentally tried to enter a ride early and I was 6 min too early..CM told me to just wait another min. So as soon as my watched changed to 5 min early, I entered.