I stayed in Bruges for 3 nights on my recent trip. We thought that was about right to enjoy everything in that area. I do not think one night is enough. I would spend a minimum of two nights. There are so many things to explore. When you at least spend a few nights it is fun. You are busy during the day with lots of activity and there are tons of people, most of whom I noticed were in big guided groups just there for a few hours. Then in the early evening, those day tourists leave and then the whole town becomes very peaceful where you feel like a local with many restaurant options for dinner and great beer!
On a related note, I cannot imagine taking one of those 12 hour bus tours to Bruges from Amsterdam. Basically 7-8 hours of the tour is sitting on the bus round-trip (depending on traffic) and you get to spend only 4 to 4 1/2 in Bruges if you are lucky.