Now, if the membranes start looking yellowish/brown and leathery, then it doesn't matter how long it's been, I'd pull it out and moisten the membranes and make sure that the inner membrane is not gluing itself to the chick. The only time I have had membranes start to dry out like that is during an assist when a big area of membrane is exposed and when you have a big exposed area you are more likely to have drying of membranes no matter how high the humidity or rather or not you open the bator.
I have some pictures of membranes that are bright white and tight.
-Kathy