The fun thing about bunkers is they have to be ventilated.
Imagine if there was a guilt-free hole in the ground. You can toss whatever in there and its OK. Dirt. Rocks. Used oil. Toxins. Trash. Bodies.
That’s what would happen. And you can’t guard it that effectively, because you need guards around yourself. I think you’re right, and a day is all it would take. A week at most.