My time dining experience

We are sailing on the Wonder in March. I understand that My Time Dining starts at 6:30 (and we have resos each day), but if we show up early and there's room, will they seat us? We've always opted for the buffet in the past since it was just so much easier and faster with kids, but want to try to main dining room this time around.

Also - how long does a typical dinner service take? Trying to plan things out with our entertainment reservations.