If you mean by ahead of time you can only make dinner reservations when you check in. We always do that. Usually the first night you don't have much of a choice,but after that you can pick where you want to eat every night
You cannot make dinner reservations until you arrive and check in
Be prepared for May or June, at least with our experience that usually the early dinners are booked. We always got the later evening dinner, which was ok with us we just had a late lunch. Once you get there go to the desk and get your reservations.
Last time we arrived on a Sunday around 3:00. After checking in we went ahead and made all of our dinner and spa reservations then for the whole week. Im glad we did because sometimes the desk has a line of people waiting to do this. The only thing you can't make far in advance are the water activities.
We have booked all our dinner reservations at the same time at CSS. I guess it depends on which resort you are at and how booked they are. At CN they did not let us book the Ohtilite (sp) more then twice during our one week stay
We make dinner reservations right after we check in. I think you can make reservations only two ahead at a time as I recall. No problem working it out though. Plenty of places to eat. Last year when Feathers was booked at the time we wanted for a birthday dinner, they told us they'd try to work it out and they did!