Hi Julian. Welcome to the wiki.
My experience with shuttle services is that you tell them when your flight is and where you are flying out from and they will tell you when to be ready for pick-up. Make sure they understand it is an internantional flight and when you would like to be there and they should be able to accomodate you.
Sacramento to SFO is approximately two hours, but you might want to allow for more time as traffic can be bad. More on weekends and during rush hours (8 am - 10 am and 3 pm -7 pm). Another option would be to take the train (AMTRAK - Capitol Corridor) to Richmond and then take the BART (Bay Area Rapid Transit) to SFO. Cheaper, but more of a hassle.
Good luck!See my comment with yours on the Davis Airporter. —Art (Bruce)