I freshly laid egg doesn't have an air cell, resting them allows the egg to dry out a little and develop the cell.
Ok. I was thinking tomorrow would be the last collection day, and during the night (so around 12 hours after the last collected egg) I was going to set them. The humidity is too high though, so I might need to wait a little longer. Are 12 hours enough, or should I stop at today's eggs?