Hi Tia, if this is important to you then you might want to make sure you cancel before the penalty phase sets in. Everything you said is pretty much the way Oceania is. Breakfast in the Terrace depends on whether it's a port or sea day, and what time they dock or anchor. Usually between 6-7 am opening and closing around 10am. GDR will be between 7-8am and close around 9:30 depending on opening time. As Lyn said, Waves is open a little later, and you can eat there in the afternoon. They have burgers and hot dogs, and a few other sandwiches. I haven't been on Princess in over 20 years, they were a one and done with me, but I somehow doubt their grill would be as good as Oceania, but if you don't want a burger or similar then you'll be very unhappy. The Terrace is usually open for lunch between 11:30-2. The only 24 hour food availability is room service.
Oceania is a whole different mindset than mass market lines. It's not for everyone.