How Long Should Fish "Sleep"?

Just bought a second tank, but long story short, unlike my first tank there's not going to be a lot of natural sunlight on the tank.

My 60G is as such
5 hours indirect sunlight, where the fish are all out swimming in the morning. Whenever the sun comes up until about noon.
8-9 hours of T5 light.
About 10 hours of darkness at night.

The problem with the new tank is, I'm going to be losing that 5 hours of sunlight. So, I assume they won't be put swimming like in my 60.

So if they're only getting 8-9 hours of tank light and then moonlight, will they be in hide/camouflage mode for 15 hours?

Is that too long for "darkness" for some reason it seems mean to have them hiding and in camo-mode for that long :-/

 

If there are windows in the room, they will still be getting plenty of light, even if the sun is not shining on the tank directly or indirectly.

OTOH, the sun only shines 12hrs per day/365 on the equator; fish, say, in the area of the U.S. seem to adapt ok to 8 hours daylight/16 hours night in winter, so I don't know that it makes any difference. FWIW, someone mentioned just a week or two ago that they don't use supplemental lighting at all with FO- their tanks just get whatever light is in the room, and they do just fine.