Don't know how this could work. First of all, deck 8 is American Diner with it's own special menu. Deck six consists of two seatings, currently set at 500 and 730 which could be shifted once the ship relocates to the Caribbean. If you show up at 630 on deck six, there aren't going to seat you until 730 unless they are just blowing smoke about it being traditional seating.
Deck seven is Dine My Way, consisting of a combination of reservations as well as walk in. If you're doing walk in, expect a wait, unless you show up before six or after eight and even then there could be a wait depending how the flow is on that day.