While I haven't had a kitten open the eyes at 2 days old, it has happened before at 4-5 days, so to say that is unnormal, may be wrong.
Is there any discharge? Does the eye look puffy?
You might call a vet and speak with them, just to rest your mind. Taking in a young kitten to a vet, should be a last resort, as the kitten's immune system is being exposed to many different things at the vets office.
I hope it turns out it is nothing. Hopefully someone with more experience than I can also come and tell us if this is normal.