If you have fish only, it matters not how long you run your lights for or when you turn them off. Just don't go crazy and make it perpetual daytime for your fish. You can have it turn on at 12pm and end at 10pm if you'd like.
Although, it's interesting to add to the natural sun light cycle, if your tank gets some ambient light in the room it's in. I have actinics on at 9am, 1 halide on at 11am, 2 halides on at 12pm, 3 halides on at 1pm, then at 5pm 1 halide off per hour until 8pm, then actinics stay on until 10, and then moonlights on =)
check out the 2nd link i think.