For that AN line, give ½ml per qt as seedlings. You will want to start by reducing their recommendations in half (or less) until you determine your plant can handle heavier feeding.
And how sooner would you be thinking it should be started I have black growth on the seedling I was thinking was dieing so I think it’s coming to a end but the other one has a little bit of yellow on end of it but otherwise looks like its growing nicely
After NPK, calcium is the most important. It should be in every feeding you give. Check out your base nutrients and see what they have in them for calcium and magnesium. At this stage your plants might only need 500ppm of nutrients or less.
You don’t need to add the two elements together, though. That’s how a lot of companies bottle them. It’s up to you to decide what your plant actually needs and give it that.