How long to you wait on partial credit refs b4 cashing out?

I have quite a few refs on a couple different sites who are sitting on 1/2 credit, 1/3 credit, etc. How long of non-contact (me emailing them, messaging them etc) should I wait before requesting approval and basically leaving them stuck with partail credit? What if they green after I get approved, do you think I should still pay if they were out of contact and suddenly demand payment? Thanks for any input you can offer... )

Well I usually say up front, need to be completed by this date ____

But I give it about two weeks. If you have been constantly trying to contact them and they are reading your PMs and not responding I would contact a moderator.