I think they let you in with plenty of time but I can't tell you exactly as I don't know - sorry!
If it's any help, we had an 8.10am ADR at Tusker House on a day AK was due to open at 9am. We were allowed through at 7.45am but there were people going through whose ADRs weren't until 8.30am / 8.45am. (At AK they were checking names & res. numbers)
We have a breakfast at CRT on Monday next week!!!
xxx