Nissan say 10,000 for oil and filter changes, I do it at 5,000 just cause oil and filters are cheap compared to a ZD30 rebuild.
As for gearbox, diffs, & transfer, every 40,000ks for these.
Be sure to check your front wheel bearing pre-loads too, when I got my Nav they looked like they were never touched since new, this involves pulling off the free wheeling hub. Removing the circlip on the end of the drive shaft and removing the hub spline/bearing assy., then removing the 2 philips head retaining screws on the main bearing nut, remove the out plate that the screws go through, nip up the nut as tight as you can and give the hub a spin, then undo the nut and lightly nip it up again to where you can align the outer plate.
This can be fiddly sometimes, as you can get it where you think it's right, but then put the wheel on and still feel some slop in the bearing, so test fit the wheel on before re-fitting all the bits back together.