Brunch, and I think High Tea, are served only on sea days. Dinner is served each night. There's really no set formula for what is or isn't a good time. When you say you want to limit the times, I'm not sure what you mean, but you are asked to give three choices of date and time for dinner, and you usually get on of these. If you don't want to eat on a certain day, don't list that day as one of your choices. You can list something like:
Tuesday, 7:00pm
Tuesday, 7:45pm
Tuesday, 8:00pm
This way you'd most likely get dinner on Tuesday night.
My only suggestion would be not to go on the last night of the 7-day cruise. We did that once, and by the end of the trip we had eaten so much rich food that I didn't really want any more.