I have to counterpoint on some things mentioned, in my own newbie to DIY experience (and not newbie with pre-made vendor juices):
In my experience, heavy alcohol content in a mix can sometimes benefit from off-cap steeping for more than 24 hours. Does the flavor diminish? Probably to a degree. But, if you are not using heat and only the time method of steeping, then it's your only option, really. I have had single flavor test flavor batches that would not shake off the floral or chemical note, even with cap off, even with 1-2 weeks of steeping. Those may or may not benefit from heat steeping.
That said, I haven't tried heat steeping with cap-off yet. And I know some of you have done extensive steeping research, and I'm not minimizing or even arguing with those results.
Tobacco mixes can sometimes get better the longer it steeps, or with UC/heat combined (My UC heats the water, so it does both at the same time). Without UC/heat, I have had tobaccos take months to shine. Not all of them, but a few.
I do disagree that with clean nicotine, everything is vapeable right after mixing. Because it's not just the nicotine in question, it's the flavors themselves and distributing evenly throughout the bottle, as well as needing time to come to fruition. And I don't understand how people vary on this point. Except I guess it's the same as people liking steeped mixes at different times steeped, or people liking fresh spaghetti sauce, or leftover. Even my fruit mixes benefit from steeping. Not a long time, but a day to a week. The flavors just settle (to my palate).
What I am doing now that I have such clean nicotine though (thank you VT) is noticing I can vape a lower % of it, and also use lower %'s in a recipe. Some things are hype in vaping, but VT nic is NOT.
To lesson the chance of my nic oxidizing, I don't add it until my mix is done steeping to the point I feel it's ready.
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P.S. Don't gong me...it's only a newbie's perspective.