That's cute! It's not uncommon for fish to have regular sleep schedules, and it sounds like your Blenny has developed quite the routine maybe your kids should take notes and watch when the blenny goes down that they should go down so they can be awake when it's awake haha!
Fish sleep cycles share some similarities with humans, with periods of rest and inactivity. But different fish species have varying sleep needs, some needing more rest than others.
Our fish have internal clocks that regulate their biological rhythms, including sleep. Like our light cycle most fish are attuned to the day/night cycle in their environment and adjust their sleep accordingly. As well as If your tank gets less active at night, it might be a natural time for your Blenny to rest.
My fish kinda know that once the lights get dimmed down to the lowest level of blue that's it's basically bed time. By the time my light is off my six line wrasse is in its same hole every night and it's right next to my head and my other tanks, all my fish go into hiding as well for bed time. I also set my tank lights to be off at 930 as that's when I want to be in bed for and my lights also come on at 930 as well :)
This is spike :)
