That depends upon how quickly it grows. Which in turn depends upon the water parameters and feeding regimen the crayfish is under.
it takes about 2-3 days for crayfish to moult
leave where the crayfish is dark as much as possible the reduce stress and leave its sheaded exoskeleton in there for about a week it will eat it for nutrients
They molt because they are growing and they get to big for their shells.
Just remove what the crawfish molted from the habitat. I am an owner of 5 crayfish. :) Gotta luv em.
it's sad really but i had a few (30) about 1 to 7 days in a can with unchanged water and no food but with the proper care about 2 or 3 years