I assume you are fermenting beer wort. I've only every used the single 1/2 tsp at 10-mins to flameout. Even in rather large OG beers, I have not added more nutrients..
When I make meads, I add nutrients daily until I hit my 2/3 sugar break .. .the point where you have 2/3 of the fermentation left to ferment. BUT yeast & wine musts are not as naturally yeast friendly as beer wort. The yeast really needs that extra 'umpphf'.
I would be curious if anyone else has thoughts on this...