They do take awhile to make, and I find that no matter how well I build it , it takes 2-3 nights before I am truly warm. After that it is only every few days that I have to add more debris, plus dry it out, etc. I'll also add bark to the outside when I have it thick enough. The big tradeoff is that I don't have to waste energy gathering more wood to keep me warm all night in a bark shelter. I have also heated football sized rocks and brought in as a space heater (keeping it away from the debris!) for really cold nights, or when I wasn't able to make it as well as needed for the temperature. Also used heated rocks in thatched huts.
I have built them after dark, but it's much slower. Another method is to make a big leaf pile (or pine needle) and just crawl inside that. With some bark and/or hemlock boughs on top, it'll stay pretty dry and get you through the night in a pinch. I learned a good method of gathering the debris while I was a kid from watching my pet skunk. He used to "borrow" any clothes left lying on the floor, and would gather these up and take downstairs to his nest behind the dryer. He would gather up as much clothes as he could in his front paws, and then pull them backwards to his nest. I adapted this for debris gathering. I get down on all 4's, gather up as big of a pile in my arms, and then scooting backwards and raking them towards me, I can usually keep the pile the same size (if not bigger) by the time I get back to the shelter and then toss it on. also a forked stick as a rake helps a lot and saves your fingers!
A way to increase the amount of trapped air is to alternate 6-8" of debris, 6-8" of small branches, more leaves, more branches, more leaves, etc. This also helps to make the debris go farther. Just makes sure that all the holes are filled, and after a few days and a couple of rains, you'll need to patch it up. The last layer of leaves that I put on is about 1'+ and when I patch it up, just use debris after that. If there is snow deep enough for a snow tunnel, then I'll make one, or just jump into a snowback, enlarge a hole big enough to sleep in, line the bottom with a foot of boughs, and cover the top with limbs/boughs/bark etc. It's a bear making a debris hut with 6" of snow on top of solid frost! When I was a kid we used to make a long fire and then rake it to one side, make a browse bed and sleep on the heated area with reflectors all around.
I have also made thatched huts, but they take a while, so stopped trying to get one done the first day out. If you find yourself lost where it's been logged, a log hogan/cabin may be doable quickly with bark/ debris/ mud/ grasses to fill in the cracks. A Lean-to with a fire and reflectors can also work.. Again, the more debris piled on, the better, both for holding in the heat and keeping dry. I'll make a browse bed and use debris for my blanket (or a thatched grass mett/sleeping bag). Also a small entrance opened out to a fire with a big reflector behind it and to the lean-to to trap in the heat. sleeping long ways to the fire is warmer. Always pay attention to the fire once you start adding debris! That's when I'll switch to rock heaters. I find my lean-to's usually end up as a debris hut anyway (or my debris hut starts out looking like a lean-to.
All in all, it comes down to location. If you have lots of firewood and little debris, it makes the choice for you.(and vice versa). I have been in more situations where I knew I could make a fireless shelter where my body heat does the work, versus getting a fire started for sure, and having to make that important first choice correctly, I'll usually go for a good thick squirrel nest over a fire.