Everyone seems to run theirs differently.
Some run 12hrs on actinics, 6hrs of halides in the middle of the actinic on time.
I was running 10hrs actinic with 5hrs metal halide but cut this back a few hrs per day because of an algae problem. I will push this up to 12hrs actinic 6hrs halide once I get the algae under control. lfs recommended shorter light period during winter, personal preference I think.
I've never heard of anyone running more than 12hrs/day