From 10 days. If they're not showing signs of opening by 14 days there may be a problem. At this stage make sure their nest is in dim light to protect them.
I think most breeds are nearer the 14 days. You will start to see a small bit of eye opening in the corner first then they are generally opened about a day after.
(PS Hopefully you wouldn't but just in case don't ever touch the eye or try to open it, let it happen naturally)