I used to take the AirBart airport bus really often, almost weekly when I had to commute to LA, and for the most part it came within about 10 minutes (especially at that time of day), maybe 15-20. One thing though, it was often REALLY crowded at the end of the day with all the commuters flying out and a total pain for people who actually had luggage. Of course, this was over a year ago when the economy was still flying high. So it could be less crowded now without the .commers, or it could be not running as much if they have had transit cutbacks. I would agree with Lola though that you should be fine on public transit and can always get a cab. Just be sure you hop on the bus that says AirBART on it and NOT the transit bus that just reads "Oakland Airport" on its front sign. That one takes over 40 minutes to get to the airport since it makes all the local stops.