The answer is determined by what you want to do. We don't hike to the furthest spots in the parks. Our motto is, "If we can't drive to it, we won't go". Not the best way to enjoy a national park but it suits our ages and abilities. So we spent two days in the Grand Tetons, two in Yellowstone and two in Glacier. If you hike, you're going to need a lot more time than we did. To make up for our lack of physical ability we always see the welcome center and the movie first. The final thing we do is buy a professionally published book about the park with lots of pictures of things we didn't see. Works for us; certainly won't work for all.
