Legal Question in Employment Law in California

Of course they can. You have no right to work any particular days or hours. You work when your employer wants you to work. If that runs into overtime you have a legal right to overtime pay, but you have no right to be worked overtime if your employer doesn't want you to.

Mr. McCormick is correct. At-will employees have extremely little control over their schedules, due to their lack of real negotiating power. You certainly have no right to additional days in order to earn overtime.

yes. You don't get to dictate your hours, they do.