In the US, you probably know if you're an hourly or salary nonexempt employee, you must be paid time and a half for all hours worked over 40 in a week. That week is predefined, so an employer can't change it to move where your hours fall in a week.
The law does NOT require this overtime to be “authorized”. So, if you plan to quit and you wanna hose em, squeeze all the extra hours you can in.
There are 168 hours in a week. Assuming you somehow manage to work all 168 hours, your employer is on the hook for your 40 regular hours and 128 hours at time and a half. They'll fire you, but they have to pay.
You have to actually work though, not just phone it in and say you were working.