That is a problem. You should always set all eggs at the same time.
Personally, since you've got one egg you are dealing with, I would let things be as they are as you could definitely mess with the other younger eggs. High humidity at the wrong time will mess with embryo development.
You may have to sacrifice the single egg for the sake of the others.
Perhaps others with better incubation skills will have a different answer. (I've done a little artificial incubation...I do most of mine with brooding hens now.)
My thoughts.
LofMc
