Weekly, or at most, every two weeks for test U. The manufacturer's suggestions on Nebido are similar to the horrible idea that test cyp should be injected every two weeks. Nebido uses a loading phase and a maintenance phase. It took them six+ months to get stable blood levels because they were trying to minimize injections and go way too long inbetween. Just like everything else, I've seen a trend in a large spike in hormone concentration a day or two after a shot...so I'd really suggest once a week. And on your first shot, you might consider doubling up.
Part of the reason nebido works the way it does is because it's thick-- the thickness and size of the oil depot will have a big effect on how long it sits there in the muscle tissue and is slowly absorbed. My oils are thin, painless, and easily absorbed for the purpose of cycling. Since you're not doing a loading phase I assume, there won't be a massive 4mL depot that sits there. Another thing to consider is that since we all exercise regularly, oil depots should be absorbed much faster than the test subjects on those trials.