I have never detected ammonia or nitrites, but nitrates have been detectable from about day 9, it was at 100mg/l and has now dropped in the last 2 days.
Well, the transplanted bacteria are definitely going to play in your favor. It still seems unlikely to me, but I guess it's possible enough bacteria was "transplanted" in the rocks, bogwood and such to keep ammonia and nitrite undetectable with a bio-load of only five danios. I still think you should have seen measurable amounts of ammonia and nitrite at some point, though. I would've expected a "mini-cycle", at the very least. If you are feeding the fish very sparingly, maybe they're not excreting enough for ammonia to have accumulated measurable amounts yet (though I think even this is unlikely)?
However, the part that really has me baffled...
*scratching head*
Your nitrates were not detectable, then detectable at 100 ppm, and then dropped down to 50 ppm? That doesn't sound likely. First, 100 ppm is a lot of nitrate. It should take a good while to accumulate that much, especially with as light a bio-load as you have. Second, nitrate doesn't "go anywhere" (to my knowledge) unless you dilute it with water changes. Once it's in the water it stays there. It only leaves the tank when you siphon water out. It shouldn't go down.
Are you certain your test kit is accurate? Those results give me serious reservations. Things just aren't lining up right.
If it were my tank, I would keep monitoring water parameters for 7 to 10 more days. I wouldn't feel good about putting fish in there until my test results were consistently indicative of a cycled tank. IMHO, there's not enough consistency in the facts thus far to convince me that cycling has completed properly. But that's just me.
pendragon!