It takes me hours to finish out a sheath across several days.
You've got to cut the pattern out, cut the welt, contact cement the welt to one side and let it set up, mark your hole spacings, punch holes through one side of the sheath and welt, fold the sheath over and contact cement it, let it set up, finish punching holes through the second sheath side, sew it up, run the overstitch wheel over the stitching, wet mold/fit the sheath to the knife, let it mostly dry, even up the edges, run the edger over all edges, and burnish them, deglaze the leather, dye it, let it dry, hand buff to remove excess die, apply gum tragacanth to the edges and re-burnish, oil it, and then hand buff it again.
That's a quick summary of the way I make sheaths, and I'm sure I've left something out even in that list. There are surely better ways to do things or different orders, but that's how I've learned. It's a lot of steps, and to make a quality leather sheath, you've got to take your time and do it right. My sheaths are still ameature at best, but they sure beat what I use to make. Here's one of my more recent sheaths:
Contrast my work to an expert's work. This is the sheath Paul Long made for the Bruce Bump auction knife:
Paul, I hope you don't mind me using this picture. I copied it from Bruce's forum. If so, just let me know and I'll take it down.
--nathan