How long should I wait?
I would suggest depending on what day of the week you begin the negotiations to be patient and wait anywhere from 3-7 business days. If you start negotiating on Wednesday, it may push further into the following week as most decision maker's are hammered from a scheduling perspective on Monday's.
Also, you need to factor in how much more you are asking for (more time off, more cash, etc. as it all has a cost). This amount may surpass what the immediate hiring manager is able to do without further approvals. This could add several additional days to the process due to travel, vacations, sickness, etc. In other words don't have a hard and fast timeline in your head. Be patient.
On the flip side, if your only asking for a small additional concessions, then I would expect this to be handled typically in a couple of days.
In short, the further apart you are in the negotiations, the longer you should expect them to take.
The negotiation process, a good read.