what is the "proper" wait time?

[smashfactory]

say you offered a domain to someone in the domains wanted section on monday. and on friday you have not heard back (you assume he isnt interested) and someone else offers to buy it. how long do you wait for the first offer you put out? do you just sell it to the second guy? email the first and let him know?
i think when you email the first buyer- even if you do have a buyer, they think you might be pushing them.
what is a reasonable amount of time to "hold up" an offer?

 

[Biggie]

if you have not heard back from a party in 5 days, he/she is not interested imo.

move on and sell to the guy/gal who has the money