please be patient. I think by "eggs developing" you mean the color will change to dark or brown, right? This is not necessarily a sign that they will be hatching anytime soon. It just indicates that they are probably still alive. Even then, it can take 1-3 weeks, because some caterpillars spend a lot of time in the eggs. Wait until they hatch, then add privet (preferably Ligustrum vulgaris) and remember that the animals tend to come from the south. As soon as the privet is no longer usable for you, they go into hibernation on their own and when the time comes, you can write to me again.
Best regards and don't panic, this speciem is (relatively) easy to rear.