Polls are open from 7:00 a.m. to at least 8:00 p.m. Anyone in line at the time the polls close is allowed to vote.
You can find your polling place here, read about the ballot provisions here, and find all about voter fraud here (PDF).
Voters have the right to cast a provisional ballot even if their name is not listed on the voting rolls. If a voter is at the wrong polling location and has time to get to the correct polling location before polls close at 8:00 p.m., they should go to the correct one and vote with a regular ballot instead of voting with a provisional ballot at the wrong location.
If you declined to select a political party when you registered to vote, you can still vote for Barack Obama (or any Dem) if you request a Democratic ballot from the poll worker. Make sure you mark "Democratic" in the appropriate space or the vote might not be counted.
Voters have the right to return a completed vote-by-mail ballot to any precinct in their county.
If you have any difficulties, you can call the California Obama Election Protection Hotline: