This varies depending on the approach used - external versus internal as well as if skin is being removed concurrently through an external approach. Also, it depends on the expereince and technique of the surgeon. That being said, the amount of time it takes to do a surgery does not necessarily reflect the outcome of the surgery! Go to a surgeon that you trust and has a reputation for good results. Good luck!
Web reference: http://www.EYESandLIDS.com