How long does Attacus Atlas stay in it’s a cocoon?

I'm assuming the low end of your temperature is a night time low. Humidity may be a factor, try misting the cocoons several times a week,
enough so they get wet. Some claim soaking in warm water can trigger emergence. These moths come from places with wet and dry seasons,
try looking up the weather in the source country.
Exotics are at least in my experience problematic with emergences, sporadic hatching is more often the norm than the typical synchronized
hatchings we get with our natives.
Every time I've had Argema(s), Attacus species, some of the African species which burrow as mature larva, the emergences are always
sporadic. You can certainly get lucky, but it's no guarantee you'll get a pair, even out of a dozen.
The moths may stay in their cocoons for several months or hatch any day, at least with atlas. They'll hatch most likely
but when is anyone's guess.