The time varies depending on the person. I know when I was younger I have months for a guy to make the move. Now I give about a couple months, depending on where I am in my dating situation. Because if I am single, I am going to try to make some moves myself. If a guy does not take a hint or show interest, I be pinning for him forever. There comes a time when a girl has to move on if a guy is not showing that he is interested.
I don't think anyone, whether guy or girl would want to wait forever for a guy she is interested in, if he/she makes no sign that he/she is interested in her/him too. I know that sounds kinda harsh, but everyone wants to find someone, and when the current situation is not working sometimes you have to find someone new. It doesn't mean you can't still make your move. Maybe talk to them. If you are still interested there is no harm.
I know I have gotten emails from guys who I went to high school with. Now they only want to hook up, but I guess they liked me back then too, but never made a move. But now I am in a relationship, so its not going to happen with them :P Plus they only want sex and I want a relationship.