Sorry, yes, I forgot the candling bit!! Yes, I'd candle them to look for a little shadow in the air cell. No need to candle all of them if you have a lot (how many are in there?). You can just do 3 or 4 to get an idea of how they are going.
I know the rule is 'don't open the bator!!' but, to be honest, if the ducklings are strong and gong well then opening the bator won't matter. It is important that your humidity is up though (70 or so) and that the incubator is capable of raising the humidity reasonably quickly once you shut the lid again. So I'd just give it a go. Be quick as you can but handle the eggs gently.