Maybe a year. The idea is so that we don't all dump them at once and cash out. That would cripple a stock. If we are forced to hold for a specified time (to be announced) then that will stagger out the time that people start unloading. The pps at that time might even be an incentive for people to hold or even accumulate depending on the performance of the stock at that time.
There is only one success - to be able to spend your life in your own way