Time it'll take to build and calibrate directly relate to your skills. You will need basic skills like handling tools, soldering, basic understanding of electronics, organization, and the ability to follow directions (you have no idea how many lack the last one).

I came from a tech heavy background, working a lot in laptop and desktop repair/building and it took me about 5 hours to assemble the Prusa i3 and another few days to really tune it in.

Don't let that scare you though, anyone can build a functional RepRap if given the correct tools and directions. Best advice is to stay organized and take your time.