Anyways, I decided to find out for myself. Since pressure ulcers form on or near a bony area, I chose to press my finger against my shin bone for two hours. So, that's a picture of my left shin (please ignore the dry skin - my foot directionally to the top of the picture) with my right forefinger next to a healing area. I started off on my experiment with gusto, with a timer on the table and a football game on TV. My forefinger waged war on the skin of my left shin. After about 3 changes of possession in the football game (about 15 non-football minutes), I got bored with my experiment, convinced myself that I was not going to prove anything, and quit. Soon thereafter, I completely forgot about my experiment.
Next day, I am in the shower, soaping my legs... hey, what in the world?... what is that dark spot on my shin?... uh, isn't that the spot I was pressing?... my finger fit perfectly into that dark depression! I had a pressure ulcer! What amazes me is that the skin damage that I caused many months ago still hasn't healed completely. Conclusion to my experiment? I still don't know how long it takes for pressure ulcers to form, but I now believe that anyone, including a healthy person like myself, can develop pressure ulcers in a short time that will take a long time to heal.