It varies quite a bit Dave, both between species and with temperature. Attacus atlas takes around 2 months to go from egg to cocoon at 80 F. Most species take around 1 and a half to 2 months. Argema mittrei take around 3 months (the larvae get over 6 inches long and 2 in diameter :shock: and A. atlas larvae can reach nearly the same size). Keep A. atlas warm and humid in all stages. The timing of their emergence from the cocoons is very unpredictable...I have had siblings emerge 6 months apart. One way to get matings of that species if you get lucky and have a pair out at the same time (you can put them in the fridge for up to a month to keep them alive when waiting for a mate to hatch), is to hang sheets on the walls of a bathroom and place the pair on the sheets, then once they settle down and stop being active - run the shower for a few minutes to get the room steamy....kill the lights and by the next morning you may have a connected pair.
