We have been there when the train has been a bit late. As B243923 said, you wait in line on the side of the road since they cannot start loading until the previous train has been unloaded. An attendant will go down the line giving the cars a number and giving you an ETA. If you are in the driveway section of the line, they will allow you to leave your car and go into the terminal. They will make an announcement when they want you to return to your cars.
According to some YouTube videos I’ve seen they have served dinner into at least 11pm. If there has been dinner service the night before and your train was delayed (we had 6 hrs one time) they gave us a snack box around lunchtime which included non refrigerated/non heated items like nuts, hummus, brownie, and other small items. I always recommend bringing a few protein bars and your own selection of snacks just in case. In our 3 round trips, the one 6 hrs delay was the worst which was due to weather with trees on the tracks. In our experience, a few hours delay has happened, but the 6 hrs one was an outlier. I wouldn’t worry too much much, but bring snacks in case.