Well, only the making part, I'm sure they all take about the same amount of time to use...
Made a piece of wood 3/8" thick, mounted up 3/8" worth of dado blade in the table saw.
Took a piece of scrap ply, drilled a couple of holes in it and mounted it to my Incra 1000se. Raised the blade to 3/4" about the table and made the first cut. Put a chunk of the 3/8" wide wood in the cut out. Slide it over a bit and used another piece of 3/8" wide wood to get the rough distance to the blade. Made a test cut, needed tightening up a bit, so loosened the bolts I mounted it to the fence with a bit and badabingbadaboom, There you have it, a box joint jig!
(Oh and I messed up a bit when I made it. This one goes from right to left when using, as opposed to the traditional left to right... )