How Long Does a Counteroffer Last?

I hope your counter-offer contained a time limit.  You are bound by it until either it is answered or the expiration date you included is up.  Until then, you'd be in trouble if you accepted another offer, no matter what its price or terms, because the first prospective buyers could accept your counter, and you'd end up in a fix, legally obligated to sell to two diferent parties.

If your counter-offer did not contain a time limit, and it came to a legal battle, the courts would probably say you were bound by your counter for whatever length of time is typical in your area.