First Grow! Fast Buds Xmas Babies

looks fines to me, some seeds have weird looking cotyledons "baby leaves from the sprout before true/mature leafs form". Sometimes they die out early other times not. Your plants looking healthy and I would not worry about it. Best of luck on your grow.

You should do a little research into DLI for your lighting during seedling/early veg. With a 240w light (if it's actually a true wattage rating) you should have plenty of light to not run a 24hr cycle. If you're really just entering your 1st week of veg, I don't think you're behind and you're not seeing the kind of stretching that suggest that you need more light. On the feeding, the seed itself has enough nutrition for the first week or so above ground after that, obviously in coco you'll need to make sure they're fed regularly and consistently. I assume since you're working in coco you've signed up here: https://www.cocoforcannabis.com/community/ It's really the best community/source of info.

Those are fine. First pic has some residue on it. Definitely not WPM tho. No worries amigo

got to agree with @ezzjaybruh With so many companies and formulations now, it might be best to follow whats on the manufactures website and bottles. Then when you have a bunch of clones to experiment with try and see if it makes a difference by running a small two part study. Best of Luck and Happy Growing!

Given what you said earlier, I think your on the right track in slowly feeding them and keeping and eye on the progression. That this yellowing could be the result of all the watering from flushing it got in the previous few days from as a correction to high salts and EC of the medium. Keep us posted,

Having significantly lower runoff than input, as well as higher pH from run off seems like it’s hungry personally. Something is almost immediately displacing that feed and spiking the pH. So it could be the roots are hungry and quickly up taking the feed, or the coco could be stealing some of the feed if not properly buffered. When the dissolved salts in the feed are immediately displaced, this causes the pH to go up because most nutrients are slightly acidic. I know it’s weird you have slightly burnt tips but that’s my best guess is up the feed a bit, or double frequency of feeds..

normal for soilless to get some brown in their tip going into flower. So many changes going into flower in soiless that this usually happens but it settles. if your still running 24 hours I would cut them back to at least 20/4 personally, so those buds get big. plants do a lot while they rest. check your runoffs waters ph and ec levels, I would try to keep it about 600 ppm and when you see flowers form, bring the ph up to 6.2