Okay so I'm going to give this one a shot, not exactly scientific, but makes sense in my own head. LOL
I've tried all different methods of trying to steep faster. Blow Dryer on Cool, as well as hot. Putting them in the fridge @ 50-ish degrees. Even the freezer, nothing seems to work. I've even gone as far as warming them up to about 85 deg then quickly cooling them in an ice bath, thinking maybe it would be like Jello and set better. NOPE.
My only conclusion to this would be in the Ethyl Maltol (sweetner) found in most mixes or nic juices. And like others have said, some things do taste better when letting them set for a few days for those flavors to really react and take on traits of one another. Like Soups. Stews. Chili. Pot roast. and fine wine. AGING is what makes them best.
Maybe it has some form of gelatin/glutans in it that, like food, need to set? I took this from a food website to kinda give you an idea as to maybe WHY it needs to steep/set for a few days.
"One was that soups made from soup bones may benefit from a night in a refrigerator because the bones contain a natural gelatin, which may set a little more with time. In this case, he said, the difference would be with an improved texture of the soup. His other idea starts with the ingredients that are found in many of these dishes. Mushrooms, tomatoes, carrots, and beef all are high in free glutamates, which are amino acids. Glutamates are key in creating the taste of savoriness, which is also known as umami. Given time, the free glutamates found in mushrooms, for instance, might be able to blend with the other items in the meal. That way, instead of getting the savory taste of a mushroom only when you bite into a mushroom, you will also get it throughout the whole dish. Which sounds like a fancy way of saying, the flavors all come together the longer they sit, they all complement each other."
Now we just may have a possible scientific explanation. ^^ I think this applies to the ingredients used to make flavors, pre-mixes, and nic bases. But hey, I'm no scientist. LOL
I think it does come down to the malic acid and ethyl maltol, but again I could be wrong.
But I've noticed a fresh batch vs a new batch gains these traits:
thicker
darker
better aroma
top notch flavor (combined)