If you're in CA, I know their labor laws are weird, but I'm fairly certain that they would do everything in their powers to keep you out of anything past time and a half.
My store does everything possible to avoid overtime.
We had a GSA (who occasionally works GSTL and Cash Office) end up with 6 hours overtime on her last check and no way to explain it. She ended up having to talk to the STL, who was not really pleased.