The whole thing took me a couple hours the first time. Pulling the OMP isn't difficult if you get the airbox out of the way. If you remove the radiator shroud & fan, that makes it even easier (although the time spent removing those may not make it worthwhile unless you're taking them off for another reason too). Remember to add some 2-stroke oil to your gas in the tank before doing the rebuild, since when you take the OMP apart & drain all the oil out of the lines, it can take 15 min to a half-hour of running (even with the control shaft held up) for it to fill up and start injecting oil again.
Are you rebuilding the lines too? There had been a thread on RX7club about doing them, and the supplies were all pretty cheap from McMaster.com. Its a good idea to make sure the check-valves in the oil injector nozzles are working properly too (you should be able to blow through the vacuum nipple, but not the other way).
The oil may be leaking from the front cover gasket, front main seal, or one of the connections for the oil cooler, or the oil return from the turbo if you have one, and all look like its coming from the same place too, so that's something to check while you're in there as well
