Home Owner, Anza Vista, San Francisco, CA
Overnight usually isn't a problem. I don't know of any areas with parking restrictions for overnight. The Residential Parking Permits regulate who can park between certain daytime hours; I believe it's between 9am and 6pm. Cars with permits may park for any period of time that is otherwise legal (e.g. not during street cleaning times). Cars without permits may park for the posted limit during these hours, typically two.
Street cleaning may begin earlier than RPP hours, however, so always check the signs. Both RPP requirements and street cleaning hours can vary block to block, and they can change, so check every time.