I was on a tiny seat for roughly three hours a day over the summer, and noticed a considerable lessening of pain after a month or so. Like you, I was used to cushy mountain bike seats. Though come to think of it, ever since my old mountain bike's seat was stolen and I had it replaced with a cheapo one, I never could get very comfortable on the mountain bike. Even for 4-5 mile rides, whereas it took usually 15 miles to feel discomfort at all on my road bike.