Dining plan or not, makes no difference. There is no set time which you are required to keep when occupying a table. Holding one in a sit-down restaurant for hours past regular dining time (for example to watch fireworks) is generally not done. Not sure what they would do if you indicated that you were finished ordering and eating, but just wanted to sit at the table for another hour or two. I'm sure some do it, but if everyone did it, there probably would be a time limit on tables.