We've sold two contracts. One was at asking price, so there was no negotiation. The contract was sent to us and we signed it and faxed it back within about an hour of receiving it (had to read it over to make sure everything was correct).
On the 2nd contract we received several offers (over successive days) that were so low we didn't counter--we figured we were so far apart, there was no need to waste anyone's time with a counter. Then we received an offer that was still on the low side, but not so far off- so we countered (within an hour) and the counter was accepted by buyers a couple days later. We received the contract while DH was at work. This contract was signed and faxed back after DH returned home from work.