Not a bad idea. I was initially concerned that you might be running them for a longer period, but 9 hours is a good starting period. Running them as you stated might give you some different looks that would be cool. Worth a shot.
I am building a stand and canopy for a 75/90 that I will be getting soon. I was planing on getting 6 X 55W PC lights from http://ahsupply.com
. My plan was to have a front row of either 6700K, a middle row of actinics (for dawn/dusk effects and fish colors) and a back row of 10000K. It never even occured to me to have the different rows cycle on or off to acheive different light levels. Good idea!