It depends on how busy the restaurant is when you get there.
If you are going to a popular restaurant at a popular time, you will lose your spot and you will probably be treated as a walk-in. If the restaurant is not that crowded it will be no big deal, but most TS restaurants are very busy and at some times of year they do not take walk-ups.
If you think you may be that late I'd suggest you call and try to re-book your ADR for a later time. Otherwise, do all you can to get there on time.
Bob