Most of the ADA products continue to produce ammonia, though the rate drops, for as long as a month.
It is sort of like a race, with the soil producing ammonia and the bacteria removing it. At some point the first species (which grows pretty fast) has caught up with the soil, and is converting all the ammonia it can produce to nitrite.
The nitrite removing species is slower growing, so unless you already had a pretty good starter colony, I would be suspicious about your 0ppm readings. These guys just do not grow that fast.
Are there some plants in the tank? Plants also remove ammonia, so the bacteria do not even get a chance to turn it into nitrite or nitrate.
Plants also remove nitrite and nitrate, and this would account for the low nitrate level.
A fishless cycle in an unplanted tank, with no starter colony will take 3 weeks and will produce nitrate in the low hundreds of ppm.