I was thinking it would probably go a lot faster now he's got material to play with. So like making the actual pieces, some surgery to clean up what's there, and then probably the biggest part would be programming and calibrating everything so he has maximum control/minimum pain. Which presumably would also be faster than when Sam did it himself the first time. Given Bucky would recover from surgery easier than most people as well it could actually be one of those snowball things where it all starts going really fast.
(PS out of curiosity does Bucky know about little James yet? :P)