Heck, many people would deliberately try to set up what you've got to get a day in AMS just to hit the windows or coffeeshops (oops, I mean, the museums...). Train links to the airport are frequent and excellent and take around 25 minutes, and from Centraal Station you can walk to a number of things (including the infamous Walletjes).

Going the other way, there's also Utrecht, a wonderfully walkable and charming sort of city. Dutch customs is normally efficient. By all means, go for it.