How old does a baby bird gotta be to open its eyes?

the kids found him after a storm and handles him way to much for the mother to take him back so I am nursing him to good health to release him back into the wild he has very few feathers that are now starting to come in and his eyes are still closed. But he is very lively, anybody have any clue on how old the thing is?

They open between 10 and 14 days old depending on the bird.

Freezing Feathers in Mid-Air