I would think the same amount of time as any other egg Nadine. As long as the inner membrane is intact, the egg shouldn't "go bad" any quicker than any other infertile egg.
Truly amazing Danny. How cool! We had something similar with one of our Spiders. It was laid outside in the garden on July 14. When I dug it up, I noted a hairline crack in it. I had read somewhere about applying glue or something to it to seal up the crack. I decided to put some silicone aquarium sealer on it. I too noted that the inner membrane was intact. Well today I was surprised to find it completely out of the shell. I checked it last night and thought it had another couple of weeks, based upon my calculation and others that we have hatched. This little stinker surprised us all and what a fiesty one. Usually baby Spiders are very slow to move and usually don't eat for a day or so. Not this one, she was moving all about the nursery and eating today. Her yolk sac was completely gone when she hatched. Here she is drinking and a picture of the cracked egg.
Notice the shiny line. You can see the crack, it is about even with the tiny piece of vermiculite.
I know it is too late to do this but I was thinking about this today at work. Could you have put something clear over the hole to cover it then set up a video camera to get a video of the development? Just an idea in case you ever happen to find another one.
Danny,
Thank you for sharing this information. I just found a a broken herman egg. The inner membrane looks intack, so I am going to cover it with egg shell.