My WW (white widow)

In soil, no, it is a baby and does not need protein shakes or T-Bone steaks just yet. Wait until it has 4-5 nodes before starting with quarter strength nutrients, moving on to half strength when she has 8-10 nodes. In soil, no more than half strength nutrients are usually required for auto flowers. When growing in soil, a schedule of plain water/plain water/feed/plain water/plain water/feed is best, once you start feeding. When it comes to watering, give enough until a little comes out the bottom of the pot. At this size, do not water again until the top 1cm has dried out again. In 2-3 weeks, once the plant is established, do not water again until the top 3-5cm have dried out. This can take anywhere from 1-5 days, depending on temps, your plants requiements and the water holding capacity of your soil mix. One of your fingers pushed into the soil makes the best moisture meter. Hope this helps, Organoman.

if the substrate had readily available nutes and one plant is smaller, it's probably genetics. it's tough to be certain of anything at this point and given the available information. the size of the plant v pot is the reason it takes a week to dry out. i don't think this is due to elevated RH%. You may find the time quickly changes in the next few weeks as the canopy gets larger. Those are pretty big pots for the size of plants. i wouldn't worry about a 6-7 days too much as it is temporary. the slightly long time it takes to dry might invite fungus gnats, et al. If you can, get some product with Bacillus Thurgenisis (israelis), aka BTi -- i butchered the species half, but you will recognize from this - there's another syllable in there. It is a bacteria that is food-safe and will kill many kind of larvae. it may take some time to colonize after watering it in. So, it's something you should start after the seedling stage as opposed to reacting to a problem in the moment (but still works eventually). It's the "easy button" for avoiding anything larvea-based. nutes.. depends on how hot that soil is. I'd wait for a hint of deficiency before starting to ramp up your nutes -- in future you'll have a better idea when to jumpstart this, if you buy the same products and the products have decent consistency, of course. i would say #2 could use some fertilizer -- can never be sure in pics.. is that a blueish look to leaves? that's P-def, if so. Assuming it isn't extremely hot soil, which opens the door to lockout and many possibilities as the cause without more information. But, the difference in stature could still be genetics. the resulting phenotypes you see of autoflowers are more volatile more times than not. There is not enough info to give you proper advice on fertilization needs. Remember it is always easier to add, and difficult to remove or dilute... be patient before adding anything. get a leaf symptom chart for reference - google image search. soil is a game of balance.. observe and react, and do better next time until it's smooth to the end with minor hiccups possible. you'll need to ramp up fertilization over time to some 'full' dose relative to your substrate and environment that will finish it out healthy and strong.