I've changed the drive oils once in just over 260hrs. I changed them at 50hrs and the fluid looked clean, no metallic sparkles, and I have just over 260hrs on it now; everything working(rear locker and front drive) as they should. Maybe I'll change them out this spring, if it ever arrives.
I’d change them now if I were you. Do engine oil/filter all at the same time and get them on the same schedule. My rear diff has shavings every time I change. Apparently that’s normal though.