If I knew the answer to the second question, I’d bottle it up and sell it on eBay. Just luck, I guess. As for the first question, the answer is 0 days, 0 hours, and 0 minutes.
I just came off of a month and a half hiatus, recovering from a bad blister. Not only is all the skin on my right big toe and ball brand new (and still healing), but all the “tough spots” on my feet have long since been scrubbed away. And yet, with only 10 or so barefoot miles since December5 last year, last Sunday I quite comfortably stayed on my feet for nearly three hours, running almost 17 miles. On “new” skin so soft it was practically begging to blister. Concrete, asphalt (old and new), rocky paths (hiked that one).
Yes, toughening happens. It’s not a bad thing – the rocks are a little more tolerable, and pointy things have a harder time sticking me. My feet get tougher, and by that I mean the skins feels more dense, just from use. There is a cost, though. With tougher feet, my impact tolerance level increases. It doesn’t hurt, or do any perceivable damage, to push off just a little and land just a little harder. That’s why it’s always good to include rough surfaces on my routes, to keep me in check. I’ve found that if I run like I have tough feet in cold wet rain, my “tough” skin comes off in a gruesome manner.
So how do I run with soft, new feet? The way I should always be running. Smoothly. Anyone wishing to try running barefoot should understand that the more sensitive your feet, the more thorough your education. Don’t cheat yourself by trying to “toughen” up your feet before the shoes come off.