The lighting isn’t likely to bother your SH.
Mushrooms are not going to like that lighting. Most mushroom’s are fairly low light corals. So unless they are at the bottom of the tank I wouldn’t do it!
Also, Mh’s put off alot of heat! You may find you’r tank temp going up even with that short of a foto period. I would recomend a fan blowing across the top of the tank to keep it from getting to hot for your horses.
If you did bump up the lighting to MH you could keep some of the higher light corals.
Maybe Pete will come along and elaborate.