I was on Edge two weeks ago under the same plan and I never even thought about it while on the ship. The buffet (Oceanview) on the 14th floor you can just stroll in whenever you please and there was always seats (offerings of course depended on time of day, during set up times only limited parts available).
The four no-extra charge restaurants-- I recommend making reservations for those in advance, or at least once you arrive on the ship-- you can do it on the app, although seemed like there was never issues getting in when I tried to stroll in at random times (they do however take dress code seriously in the sit down service restaurants, if you're male, you have to wear pants)
For the paid restaurants like Eden, definitely make your reservation in advance, I tried to on day 2/3 and they were sold out the rest of the sailing.
I'm curious if the ship being way below max occupancy makes the dining times irrelevant, but then again, had I chose a set time maybe they would have turned me away on outside times? I don't know
