Second, I think I was remembering this quote
> Limos in U.S. cities usually have to prebook an hour in advance, by law, while only licensed taxis can pick someone up right away
which may not apply to SF. Do you have a source that there is in fact no such time-limit in SF?
I've seen (and taken advantage of) black limos cruising the streets of San Francisco at busy times (New Year's Eve, closing time), picking up passengers taxi-style. It's presumably illegal, but the police generally have better things to do at these times than harass limo drivers.
I find it interesting because there is a record of SF not allowing limo services to top for customers, but I can't find any on the one hour restriction. Honestly I think that comment was taken out of context regarding the companies themselves having a one previous hour arrangement policy.