I have 2 egg cases in a glass jar with a mesh lid. I came out this morning and noticed one baby has emerged. Hours have gone by and there is still only one baby. Will I get more? How long does it take for the rest to emerge once the first one makes his way out?
How cool that you have chosen to hatch Praying Mantis nymphs!
Keep watching your egg cases: there "should" and may still be more. This article from Iowa State University mentions that some eggs will not hatch at all. Be sure your glass jar is in the correct temperature for the best chance of all your eggs hatching.
This article provides some additional information on mantids: