When I bred a Stagmomantis carolina female that came from TN with a male of the same species from FL. The nymphs hatched staggered. Some nymphs were molting to second instar while their ootheca was still hatching. It is possible, but I can't say if any were at 3rd instar as I wasn't recording the information. I am not sure if the female was wild caught when a nymph, or captive bred before I got her.
Wild collected Stagmomantis carolina oothecae that I find and hatch here in S. FL will hatch all the nymphs within a couple of hours. When the nymphs from those oothecae were bred, their oothecae have hatched the same way. It has been the same burst type hatching with oothecae of a wild caught female from here.
With the exception of the wild caught adult female, these mantids were hatched and raised indoors at room temperature.
Perhaps it can depend on where a mantis is from and the climate that their parents have been exposed to, rather than just what species the oothecae are produced from?