When to introduce nutrients?

What type of soil do you have? It likely has nutrients for a bit as roots colonize new areas of pot. Don't be so eager to fertilize. It's a small portion of the whole equation. plus, if roots don't exist there, you fertizilize 3-4 times before that point now the roots hit overfertilzied soil and bad things happen. Wait for those cotyledons to show a hint of yellow. Start diluted in soil. Slowly build up. Observe and react to plant as you go. It dictates pace. Keep track of when you irrigate and when you irrigate with nutes for future reference when issues inevitably crop up.