The most important consideration when planning a visit to Petra is time.
With 2,640 acres in the Petra Archaeologic Park itself, there is much to see and with few exceptions you are free to explore everything at your leisure and will. The local people all agree--to properly and fully explore you need five days minimum. While there is certainly enough to occupy yourself for five or more days, two to three days is sufficient to visit all of the highlights in and around the park. One day--or worse yet a morning or afternoon--is likely to bring some disappointment to those who have traveled a great distance. If at all possible, plan for two full days as an absolute minimum.