1st grow

did you water after transplant, if not, could be too dry... if you did could be there is not enough perlite, and if you disturbed the rootball it might be in shock. lack of o2 at roots or shock.. oh with new pot is it significantly closer to the light than before? also a consideration... too much light will make plants droopy too.

With a fresh transplant you won't need much feed. The dark green says it's strong already. The burn edges is from overwatering, and likely ph change in substrate with new stuff. Which also has a potassium deficiency sign as well started. So I am really leaning on your ph in soil and the changes it is experiencing. Rapid change in soil ph hurts them. .1 ph in change is a big difference for them. They can only tolerate so much. Is why they say to water good on transplant. Plus If you use more course perlite it will make the plants resistance to overwatering much better. Roots like air as well as nutrients, and water.

I like to wait a week or two after all toppings when I flip to flower. You could flip right now, there is nothing stopping you, however if the plants are not mature yet they won't flower anyway. Photoperiods will need to reach sexual maturity aka plant puberty before they can initiate flower. its why some people grow 12/12 from seed. Some plants require a bit longer to hit that point. I find between 5-6 weeks is when they are normally ready. When you plant shows pistils in veg that is a tell tale sing is it 100% ready and as soon as you flip it will begin the transition and start to stretch in the next few days/week. Good Luck!

Thats a mag Def in its late stages. A cal mag.. But as its a mag issue a quicker fix would be an actual mag nute or better yet epsom salt

Flowering starts first sign of the flower not the day you flip, takes time for the plant to prepare the hormones, etc, normally it takes 4-5 days after the switch you see the first sign of the flower then you begin counting days., never too l8 to use foliar, the fastest way to remedy deficient nutrient, still looks to be a couple yellow hairs, once your buds stop producing those yellows almost entirely then id start checking your trichomes for cloudiness. Good luck brother Kmurr!

Those look finished almost already