Couple clarification questions

[Formernuke]

I'm using a top fed DWC system. I plan to start the seeds in a rapid rooter tray and then move them to the hydroponics.

1. When should I move them over?

2. I did a grow a few years ago but I added the nutrients too early and killed my first attempt but cant remeber the right time so when do I start the nutrients schedule and when do I start adding hydro guard?

Thanks in advance

[Toker1]

I move mine into the hydro system when my roots show.
I add 1/2 strength nutrients with hydroguard when the roots are dipping into the water mixture.