I've often thought that the sleeping habits of different fish are strange.
I have four tanks in my living room and the lights go off at 9.00 pm. The platys, the tetras, the angelfish and the barbs retire into the undergrowth for the night. The male guppies and the pearl gouramis carry on swimming about until much later - around 1 -2 am (the main room light is still on). The danios seem to carry on swimming around all night.
I also have a tank upstairs which doesn't have a timer for the light (and can't have one fitted ). It has three adult female guppies a few adolescents and some fry. I switch the light off when I go to bed - if that's early (around 10 pm) all are still swimming around. If it's more like 1.00 or 2.00 am then the adults have retired into the plants - but the youngsters are still as active as ever. So female guppies need their sleep - even if the light is still on. Perhaps they just get tired of the kids .....