Your total rehearsal hours are the scheduled times, less your lunch break. So a 2-10 is 8 hours less either 1 hr or 1.5 hrs for lunch.
The person who is cut loose early? Happy vacation for them, but since you called them until 10, their day runs until 10. Just as you would be paid for your full day even if, at the last moment, you are cut loose early.
The performance is timed from 1/2 hr to curtain down (no matter how long it takes to get out of costume/make-up).
Good luck!