On some state's real estate contracts, there is an offer expiration date. This date informs the seller when they need to respond, or the offer might go away. This allows the offeree the option of pulling out of the contract before it is signed. In a multiple offer situation, the seller might care about this date if yours is the best offer, but if it takes longer, and you are still interested, the date means little. I'd say 3 days is realistic to wait for an answer, any more and they are likely dragging it out to pull in more or higher offers.