As has been said, it depends on the blend. There's no set time. For me it's a matter of the tactile feel of the tobacco, and that varies with blend type.
English blends are the most forgiving because the Latakia and orientals pack a lot of flavor regardless of whether they're straight out of the tin or dried for hours. More details in the blend will be revealed by lower moisture content.
Aromatics are more tricky. Left too long to dry and the flavorings will dull down. This is why aros are really not a beginner's choice.
I mostly smoke Virginias, so I dry them down until they are just shy of bone dry. Crispy around the edges but still pliant. No sense of moisture welling against my skin when I pinch the tobacco. That's when I generally get the most detailed flavors from a Virginia blend as well as Va/Per blends and Va/Per/Bur blends. Mummy dust may still maintain a cereal flavor, but that's not what I'm looking for.
And some blends are more forgiving about moisture content than others. You need to experiment with your blends to know best how to enjoy them.
The most finicky in my experience is Esoterica Stonehaven. There's a narrow sweet spot where you get all of the chocolate and raisins as well as the treacle and underlying tobacco and it can be maddeningly difficult to hit.
Here's a little story to illustrate. Back when the Los Angeles Pipe Club was in its early days we had a meeting at the Cigar Warehouse in Sherman Oaks. I got to talking with one of the guys there and he started complaining about what a tasteless piece of shit Stonehaven was. After finally scoring a bag he just couldn't get anything out of it and decided to "punish" it by leaving the bag in the backseat of his car, in the 100˚ dry Los Angeles summer heat. And that's where it had sat for two weeks. He was going to throw it in the trash, but offered it to me if I wanted it.
Who was I to refuse? I gladly took the bag, figuring that I had nothing to lose and brought it home. I figured I'd give it a try and loaded a flake into one of my larger pipes. Then I lit it up.
Total magic. EVERYTHING was there. I had another bowl just to see if it would repeat. Total magic again. I jarred that bag and enjoyed it sparingly over the next year and every smoke was GREAT. I'd never before been able to consistently get the best out of that PITA blend.
As with everything else, experiment. What works for me may not work for you. Try a blend at different moisture levels to figure out what works best for you with that blend. Generalities will get you in the ballpark, but more experimentation will get you to home base.