All of my tanks have a nightime photo period simply because that is when I am home to enjoy them. Also should mention if you are only doing it for energy savings I doubt you are going to see much a difference. These aquarium lights do not use nearly as much lighting as most people assume they do.
How long should a "night time darkness" period last?
If I can assume that on average throughout the year, 6:30 AM would be when the ambient daylight starts lighting up the room (through curtains), would a 7 hour (11:30 PM to 6:30 AM) "dark" period be OK? Can I go even later?
I want to move my photoperiod as late in the day as possible because I have very hard/alkaline water so the metals in micro-nutrients (iron etc) fall out of solution very quickly, so I'd like to be home from work and dosing as close to the beginning of the PP as possible... I recently have been reading that dosing at night after lights go out (my previous plan) probably means almost all of the metals in solution are now unavailable to plants by the time my lights come on 12 hours later.