How long to lay an egg? Depends on the bird.
I have had some get in there and 10 minutes later they are singing the egg song. I have had others get in there and 2 hours later they are still grunting in the box. Sometimes I think they like to get a little extra rest and use the 'im laying' as an excuse !

Id not worry about the time to lay. The only issues you may encounter is broody, they want to sit in there all the time hatching, or egg bound, which generally happens only to newer layers and you'll KNOW because they walk like penguins if they are bound up. Again, watch for it but don't lose sleep over it.
Aaron