It's well worth staying the course and ending the day at Petra. The rocks take on a deep pink/red hue as the sun sets, plus as the site empties of people you are left to behold the beauty of the carvings in relative peace.
When I visited (April 2007) they were placing lit candles for a Petra At Night Walk - adding even more romantic beauty to the carvings and the walk back up the sique.
Is this your business?