The length of time depends on a number of factors, but it is not...

The length of time depends on a number of factors, but it is not unusual for it to take months. There is no time limit, the only limit is the patience and willingness of the parties involved.

Of course, it is in everyone's interest to come to a decision and finalise it sooner rather than later. You don't want to pay the lawyers more than you have to, and you don't want management attention directed away from the business for too long.