Nitrites, not nitrates...flack knows what the difference is. As I understand it, you take your dose about 2hrs before your run. I tried it for a parkrun one time and it made no difference, I think I ran a bit slower. They accidentally sent me another order so I had it before my pb Leeds 10k, which I've not yet attempted to better.
I always find that an appreciation of the paradigm in its entirety adds value, and that the originator requires you to fully understand the principles. I remember that my grandfather used to read the manual in full for every new car he ever bought, despite the pedals being in the same place.