Well, I normally give one week after last communication for anything like that. payment sent, agreement to pay, whatever. That is also assuming that I had not been trying to get ahold of that person and they are not online.
Most auctions and or EE sales, I give a week to send money, or for money to arrive once sent. If over a week without ANY communication from the other person ("hey I sent it", "hey I got it", etc) then I contact them. If you've already sent them IMs about it and they've been online afterwards without answering, then there (IMO) is a problem. If nothing else, it's just plain rude.