I have been going 9 - 9, but am starting to cut back a bit. I think 10 hours is a better photo period, especially now since one of my tanks is experiencing algae issues.
I find that it really doesn't matter a great deal how long the lights are on when my tanks are in balance. Everything just takes care of itself as long as I'm consistent with the ferts. Pressurized CO2 makes it easier to keep that end consistent, but the tank that's got the algae problem went through a bunch of changes recently and I'm now fighting the result.
Len