It really is widely variable, based on bowl size, cut of the tobacco, packing technique. I expect anywhere from 30-45 minutes for a bowl from most of my pipes. Flakes will go longer. GLPease blends always go on the short side. (For me, they require a looser pack to get the most from them, which means less tobacco in the bowl.)
And, yes, DGT is a real thing. But I've honestly never tasted any benefits whatsoever from letting a half-bowl sit overnight. And in order to have that half-bowl in the first place, you have to experience Smokus Interuptus, which I personally find unsatisfying.
I can't help wondering if all of this discussion is causing some folks to suddenly start worrying way too much about how they're smoking their pipes. There was a time, believe it or not, when pipe smoking was a source of relaxation and comfort. . .

Bob