The gestation period depends on the species. Some species,such as H zosterae are 10-14 days while other species can be as long as 28-30 days.
Normally when a male is pregnant, he will become very reclusive, tending to want to stay by himself. His pouch may darken and of course stay tightly sealed and grow larger. Some males will become a bit more difficult to feed and need to be target fed in order to assure he is receiving the proper nutrition.
HTH