Blatta lateralis eggs should start to hatch around 2 weeks (give or take a week) from my experience. I had a bunch of them and they were good feeders for everything besides my little storrs monitors. They never ate any of them. So i switched to crickets. Thats not a problem for you.
I actually quickly got rid of mine for a different reason. I now work at a hay yard and inside where the hay is we set up bug traps to kill the bug like weavels and other hay eating bugs. I cleaned them up and they had about 30 blatta lateralis on it dead. I later found some egg sacks in the corners of the hay. I havent seen any in 2 weeks but its also cooler. This is in southern california. I live 15 minutes from this area and so if they breed there, they will breed at my house (what i think). So i got rid of all mine. I didnt want an infestation.
I'm not totally sure that they are multiplying or just laying eggs. But i dont want to take the chance. So its up to you.
I want some more difficult roaches to breed (that i dont think will survive outside the cage) or just breed crickets.
cheers,
Sean