Not legal.
The Federal labor law on this subject is clear and unambiguous. If your employer tells you where to be during your lunch break, then you are "subject to the direction of the employer", and therefore still on the clock.
If you are in a State, such as California, where there is a legal obligation on an employer to provide an unpaid lunch break, then the employer has to pay you your wages for the 30 minute lunch, AND the penalty for not giving you a break. If you are in a State where lunch breaks are not required, then he just has to pay you for your time.
Richard