You generally use the nation sack on a man who is YOURS, whether you are married to him or not. You need some money he gave you, his semen, his hair, and so forth -- so it is not used on a man with whom you are not already real close.
As for a time-frame, that is not the way magic works. You watch for signs, see if there's movement, and then get your completion. There is no "delayed" effect thing, like, "it'll work after six months" or such. If the signs are good soon after you start, you keep running with it. Then it works for you as you work with it.
Also, you must understand that not every spell works every time or for every person. For instance, if you are the "outside woman" and his wife is working to hold him, it is unlikely that a Nation Sack would break them up, although it certainly should make him want to continue seeing you.
