Can you keep red lights on all night long? Sometimes if you have a completely dark time in your photoperiod, they learn to wait and only come out when it’s totally dark. I keep lights on 24/7- but from 7pm to 9am it’s red lights only!
The way to sex an octopus is to check out the tip of its third right arm. If it’s “stubby” then that’s a hectocotylus, it’s male reproductive organ. You can find lots of references here. So first you have to see the octopus...
If it’s a female who’s decided to brood, then it’s laying eggs (fertile or not) and will die soon after they hatch. The way to tell if it’s a female starting to brood is to watch to see if it’s building a “barricade” around it’s den, packing any shell, rocks, substrate- anything it can find- tightly into any hole of its den.
I’d set my alarm for the middle of the night and check the tank out then. Good luck and keep us posted!