Looks pretty good man, just came back from a long holiday, it could be from a number of things, might just be a bad seed, could be it was manhandled abit while it was still germinating. Personally I don't start giving nutrients in soil until at least I see the third node start to develop. If anything it would be a nutrient toxicity.
I suggest treating the roots with a stimulator, next time around. Also can I ask why did you put what I think is a nail down at day 10? I'm not sure what that is and I havn't seen it before could you let me know.
I can't tell yet, switch to 12/12 if you havn't yet you don't want those plants streching to far. If you know their females try and keep a mother plant, its better to wait it out abit and have weed forever then having to start from seed again everytime.
This looks fantastic! Whats your watering schedule? Too much can cause root rot and that'd be a shitty way to lose a white widow. Good rule of thumb, if the soils not crusty, don't water! You prolly know all this but I was just throwing it out there. Also is the glass really necessary? I just know that some glass absorbs certain light that the plants need... I think you would really be fine without it (just put up scrog screen when they get within inches of the lights..) and the ventilation would still be adequate enough to remove the heat from the lights.
Is it just me or does it look like your plants shrunk. Also how did you light seal your door? Like what material are those black bars.
The plants look pretty good but I am concerned with the temps. and the humidity. I don't know if there is a way to get more aggressive with exhausting the hot air or not; you've done a really nice job with the cab so I don't know if it's possible. A couple of suggestions and you can take them any way you want. I'd try putting a container in the bottom section of the cab with some small towels that you've thoroughly wetted and wrung out to see if you can raise the humidity. I'd also try, for now, using two thirds or even half the lights for the veg. cycle. I don't think it would hurt the growth and may even help the little guy. Sometimes too much heat and not enough humidity can stunt growth. Good luck.
Sorry I haven't been back sooner BH but your girls look pretty good. I think that maybe your WW girl is suffering slow growth because of the heat in your box, I think you might be better if you could keep the high for the day under 80 and for me 76 is the sweet spot. If I could keep it lower normally I would. Also the advice on nutes is spot on IMO if your soil has nutes in it already. To me it looks like the WW may be nute burned slightly but I am not sure because I couldn't really see all of the leaves. One of the biggest problems I have with growing 2 plants in the same container is that I can't add different amounts of nutes to each one or care for them individually if needed. Just something to consider for next grow.
Also for your screen IMO the best way is to keep the plants close to the light until you get them on the bottom shelf the whole while you should LST to have an even canopy. Once you hit the bottom let them start to grow into the screen, keep training them under the screen until it's about 70% full for your first time. Once you hit about 70% I would start trimming out the branches that aren't already to the screen or aren't likely to make it in 2 weeks growth. At 70% full you will want to flip to flower and continue training for the first week or so, after that let them go. Your only job then is to keep the canopy as even as possible (you can use string tied below the canopy to pull the branch down) with string or whatever is clever. You also want to make sure that you have air moving through the canopy because the cramped vegetation can start to mildew or rot. Let me know if you don't understand what I wrote because it seems like a lot to take in but really once you start you should get the hang of it pretty quick, good luck and happy growing.
KnB