Probation is a status given to a newly whitelisted player. From the point of view of the player, there is no difference between being on probation and having full Builder status. Builder status is given after proving oneself to be trustworthy. There is no fixed period of time to this, it normally just happens when one of the Admins remembers.
This means that once probation is granted, the player is free to head off and start mining and building.