Depending on the size of the sheath, one with a lot of beading can take anywhere from 30-60 hours depending on the amount of beadwork. I don't do nearly as much beading as I used to. I'm almost 60, and after nearly 40 years of doing it, it's getting tough on my eyes and I hate wearing magnifying glasses.
The most time consuming beading project I ever did was my peyote stitched straight dance cane from around 25 years ago. It had around 80,000 beads, give or take, and took about six hours of work per night for an entire month...170-180 hours. I carved the eagle's head handle from a piece of elk's antler.