From what I hear abaout "mountains" on the east coast, you are going to be completely shocked at how long it takes to ride from the peak of Whistler to the base. I've actually rarely done it because it takes so long and the runs/snow are better near the top so the bottom is just a waste of time.
When you ride whistler/blackcomb you typically ride only the top half, but if you want to go from the top to bottom, it probably takes 20 munites unless you are trying to haul ass.
There's a lot of good advice on this thread so definitely do a lot of research before spending a ton of $. I've been to Whistler often because I am only a 5 hour drive away. I have an amazing time everytime I go, but a lot of that is just the fun times with friends on the mountain and in the village. I've had better pure snowboarding days at smaller/cheaper resorts closer to Seattle, but Whistler has always been a fun all-around trip.
20 minutes top to bottom for Whistler is if you're a strong rider and you're bombing the whole time without needing to stop to catch your breath. Your first trip up the lift will blow your mind how insanely big it is.
3D Map of Whistler
is a great way to wrap your head around whistler, I wish there was something like that for every mountain.