VFX Law:
Overtime laws in California are clearly defined. You shall be paid overtime at the rate of 1.5x your normal hourly rate for any hour worked after an 8 hour day. For any employee working more than 12 hours in one day, each hour after the 12th shall be paid at 2x the hourly rate (double-time).
Why companies have to be reminded of this is beyond me. This isn't something you can wave your right to.