1st proper grow, who wants to teach me? 😁😊

If you started with good quality soil, it should have enough nutrients for at least 3-4 weeks, maybe more. After looking at your diary, I would suggest increasing the lighting, either move it closer or up the percentage if you have it dimmed, Your seedling is stretching due to not enough light intensity, it is not a nutrient issue as can be seen by the lovely dark leaves. When the plant has 3-5 nodes is usually when I start feeding, but only gently at first...quarter to half dosage strength is usually enough, especially for autos. Remember too......it is very, very easy to rescue a slightly under fed plant, but very, very difficult to remedy an over fed and burned plant! You could also top up the pot with a bit of extra soil, this will support the long stem better and not effect the plant adversely. Filling the pots right up to the top allows maximum room for root development and more roots = more plant. Besides, as you water, the soil will settle and compact down, meaning if you have a big gap to the top of the pot, your deep seated plant ends up missing out on a lot of reflected side light due to shading from the walls of the pot, which just reduces growth.

I agree with Organoman, everything need downtime, plants are no different. Can you grow at 24/0, sure but that's only when shits locked in and even then its hard on the plant. 18/6 is best IMO or w/e hits your DLI of 35-40 thats over 12hrs. Otherwise the plants don't look to bad. I think your overthinking it. Good Luck!