Well it really depends on how much experience you have. It can pretty quickly if the builder has done a few before. If a shop does it and they are not busy I would say it could be done in a few days. Possibly it could be done in a day if the money was no option.
Depending upon your knowledge of rebuilding motors it could take several days, several weeks, or a couple of months. If you have all of your parts it will be faster.