Considering that the fish use moonlight to guide their breeding cycles, there is no harm in leaving them on. Also, especially in a reef tank, your fish will go behind or underneath the rocks and corals so they won't be seeing the light anyway so they will sleep when they are tired.
When I return from the trip I am currently on, I will upload to my albums 2 pictures of my old artificial reef tank. They were taken 10 minutes before and 10 mins after the lights went off for the night. You'll see what I mean about the fish disappearing to sleep
( Check back to my profile in mid June.)