What happens if you have the first time slot for the traiditional dining and your excursion runs into that time frame?

I'v enotice a lot of the excurions don't end until 6:45 and i think our time is 6:15 for dinning.

You would have your choice of the buffet or one of the alternative dining rooms.
If you are going to miss your regular dinner time let your waiter know ahead of time as a courtesy.

As usual, I agree with f-mattox.

Should you book an alternative dining room, be sure to make your reservation as soon as you can after boarding -- many people may have the same idea, especially if it's a popular excursion.

Let me second the importance of letting your waiter know the day before the excursion. This will ensure they don't hold up service to the others by waiting on you to show up.