In the case of Bobcats > Hornets, it would likely be a very quick (as in one offseason) switch because there aren't many, if at all, legal hoops to go through since the League already owns the name. The hangup would be New Orleans switching to whatever new name they choose. That may very well take two years but a) it seems like that process is already underway and b) the league could shorten that time if they wanted to and everything is squared away.
The last team to rebrand was the Sonics to the Thunder, and they went through that process in the matter of one offseason. It can be done.