not necessary to tip but prepare to stand in a long line. Send someone from your party direct to dinning room as soon as you board, they will be there and usually happy to make your change if possible.
If you had a smaller party, the switch would be very, very easy because early is the seating that fills up first. Because of your requirement of a table for eight, you may have a problem, even switching to late. When you board, go immediantly to the maitre'd and put in your request. You may get lucky, and get the switch, but I'd guess the chances are 50-50.
You can always check once you are onboard, but if it doesn't work, you may find that you like the early over the late. I like to be able to do things after dinner, without finishing dinner at 10, just too full to enjoy things. Best of luck.