I cannot comment on "official" book time, but I can offer the following.
When I did it myself, I think it would have been 1-2 hours maximum if I didn't make a huge mistake. The alternator itself is held on with two bolts. The lower bolt is notorious for being a pain and the head getting stripped. I found this out the hard way because I stripped the head and then Googled it. Be sure to be precise particularly on that one.