Really depends as others noted.
Standard Osage with no knots and straight, (yea it happens), only have to go one ring down, 15 hours.
Lots of pin knots, add about 3-5 hours. Have to go down 5 rings, add 3 hours. Put on skins or rawhide backing, add 4 hours. Add horn tips, add 2 hours, nice leather grip, add an hour, on and on.
Last summer I finished a yew longbow with slide on horn tips, and takedown sleeve and I bet I had 50 hours in that thing. First time I ever fitted tips onto a bow like that, and first time I make a takedown.