I always went with 12-14 hours of 250w MH. Now I feel that might be a bit excessive so I've cut back to 10 hours and still get good growth. How long have you been keeping yours at 8 hours? Do you get good growth? I'm sure it won't hurt to experiment just keep a close eye on your sps and as long as their still growing than no harm. Eventually as you cut back the photo period your going to get less growth. I know several people that only have the MH on for four to six hours but they all use T5 or CF on a regular 12 hour period as well.