I made a video of my break-in box, and I run both boxes for about 20 minutes in each direction.

https://www.youtube.com/watch?v=AY0_CAju0yY Running or breaking in gearboxes is just running them in an oil bath for a bit to let everything settle in. Kind of like breaking in the camshaft in a rebuilt motor so the lifters seat properly, if that helps at all.