It's a good question, I had to look it up again, but it actually does matter. You can't "pyramid" the OT hours on top each other--you're owed OT for whatever is greater, the number of hours over 12 each day or the number of hours over 40 in a week. If you want to read the Court of Appeals opinion where they decided this, I'm gonna post a link.
If you're not getting paid what you're owed and/or not getting meal and rest breaks or other problems with your employer, you should talk to a lawyer. You should get a free consultation on a case like this.
The answer here will also depend on whether you bring a claim under the federal FLSA or the California state Labor Code. In California, any time worked over 8 hours a day is overtime, and any time worked more than 40 hours in a week is overtime. Thus, for the first 3 days and four hours, you would get overtime for the time worked more than 8 hours in the day. At the point you reach 40 hours in the workweek, all time thereafter is at overtime.
You never get to double up overtime for the same hour worked.
Good luck to you.
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