Something is not right here, or I'm misunderstanding the question (or answer given).
Assuming this is the scenario...
Somebody offers you $50, you counter with $500... you don't hear back, and now you wish you had accepted the $50, yes? If that's the case, you can simply make another 'lower' counter offer, all the way down to $51. You don't have to wait for the 7 days, or for the other person to reply.
At least that's the way I remember it.