when i had my colonies,i just left the eggs in the sand where they were laid,and they always hatched out, i never really kept track on how long they take to hatch,being i had soooo many in there at the time,they were just popping out of the sand all the time and the sand was not moist either. hope this helps alittle.
i offered them a small plastic box with moist peat and noticed that ALL females prefered this place for laying their eggs.
Then I removed the box and used it as an icubator, this way I had more a higher ratio of emerged nymphs.
I usualy letting the box in the enclosure for a couple of days and then removing it for incubation, but with the time its gets boring and you will get drawn from them...they breed like rabits!