If the employee is in a non-exempt (hourly paid) position, there is no such thing as working "off the clock." Non-exempt employees MUST be paid for all hours that they work.
For exempt positions, "off the clock" is irrelevant. An exempt employee must be paid a regular fixed weekly salary regardless of how many hours they work (with just a few exceptions that allow the employer to deduct wages in full day increments for very specific reasons outlined in the law.) There are no circumstances in which an exempt employee must be paid overtime.