Hello,
I start ph'ing my water as soon as they're in large containers..for some reason if i start in solo cups they haven't had any problems with just water.
With nutrients...i think it varies but sometime around 2 weeks of using watever the soil contains is when I have to start adding things in. Since your plants small and you may not water as heavy, she may get to week 3 without needing extra.
Congrats on the sponsored grow, good luck and happy growing .✌️