Rides are counted at the moment you accept them. Accept ride at 4:57pm start trip at 5:01pm. The ride will count as 4-5pm time frame instead of 5-6pm time frame.
Rph if it is 1.5 per hour and you were online for 3.5hours then complete 5 rides, 6 to be sure. When the time is from 7-10am and 1.5 per hour. 5 rides between 9-10am will count for the other two hours, as long as you remained online. Once offline, everything resets.
Most guarantees, from what I read, are based on that timeframe vs the entire week. So if your acceptance rate is low while not on guarantees, but 100% during guarantees, then you should be fine.
I had a 67% for the week, but during guarantee periods I kept it at 100%.
Hope this makes sense. Be sure to read all details in your emails.