After one week, the difference in my foot's skin was noticeable.
After three weeks, I was good on pretty much any flat, smooth surface.
After six weeks, pointy stuff and wet stuff was no longer a real issue either.
This was going pretty much 24/7 barefoot, though I think that volume actually slowed me down a bit. If I avoided moisture more initially and wore shoes for the longer Tuesdays, it would have been quicker.
I walk with a forefoot strike, similar to how I run, but more gentle. When my foot hits the ground, it lands on the outer edge of the forefoot, then rolls into the whole foot making contact, heel last. If I ever do step on something sharp, it typically results in my "feeling" it before it breaks the skin and taking a lurching step to relieve the pressure before any pain occurs. I can tell that I also reach out and grab the ground in front of me with my foot though, which needs correcting. I think I picked that up when I started running in Vibrams.
Since starting, I've only had one thing stab my foot. It was a small white rock in a parking lot, a triangle shape about 5mm long and 3mm wide with a thickness of 2mm or so. A tiny little thing. After a few painful steps I realized something had actually broken the skin, and I hobbled over to the nearest bathroom and it came out very easily, cleanly, and without any more pain. I think this was after three or four weeks, but I can't remember exactly. I was walking to work at around 5:30AM in the pitch black darkness, so I had it been light, I might have avoided it to.
I haven't had any run-ins with broken glass yet (though everyone cites that as a reason to wear shoes), but I'm fairly confident that I could handle it now if it were fairly pulverized.
If you get the chance, try walking on different sports turf fields. The grasses are amazing there - like a carpet, really. I love the feel. Not astro-turf though, since that stuff is nothing like turf (it's also hot stuff, like I said before).
And yes, I'm actually holding that handstand. Get on my level.