Hi bioteacher, I responded to your other thread before seeing this one. Usually they darken the day before they are going to eclose. I put BSTs in an aquarium tank on the kitchen table, and they usually eclose early in the morning if I leave them inside, but sometimes I put the tank outside overnight to slow down the eclosure if the weather is rainy.

I usually release them in about 2 hours, maybe more. They will start to get restless and flutter around in the tank, and they seem anxious to get out.