For me personally...the only mixes I let "naturally age", (I don't use anything like heat, ultrasonic cleaners, etc.), are the few I make that have Vanilla Custard in them. Those are best to me...after about 3 weeks to a month. Also, if a mix has a flavoring in it that contains ethyl alcohol, I let it breathe naturally for a few days, shaking several times a day...and then vape it!
All other eliquids I make, including recipes with creams (ie. Sweet Cream, Bavarian Cream, Whipped Cream, etc.), I just shake and vape. They're fine to me when first made. I don't make tobacco flavored eliquids myself, but I've heard they're best later, too, like the custards.