They usually pick up 3 hours prior +/- 15 min. So your window should be 2:55a to 3:25a. What ever your departure time is they tell you to be there 15 min prior. As a reminder at that time you will need to bring your luggage on the bus with you as the RAC will not be open.
ETA:
And the 3 hours +/- 15 min is for domestic flights, it's 4 hours +/- 15 min for International flights