If this doesn't feel better
If this doesn't feel better in a day or two, you might look at the possibility of a micro stress fracture. I don't want you to get alarmed if this is minor and short-lived. But if you can't reasonably walk on it without shooting pain after a couple days, you might talk to a doctor to get it checked out. I hope it goes away as something minor that you just overstressed. I too started in VFFs to "transition" and did TMTS, resulting in a left foot stress fracture in the front of the ball of my left foot.
Barefoot forces you to learn good form correctly, and doing bare only over a period of months allows that good form to become imbedded in muscle memory. Additionally, some of us have had the experience that the VFFs can actually accentuate problems with problem feet. My right foot feels fine in my VFFs, but my left never feels fully comfortable. For hiking and for tooling around, I love the VFFs, but not for running.
That said, start slowly (1/2 mile a day, every other day with a rest day in between) and build up after a couple weeks, adding maybe 1/4 mile per week as your soles adapt and your foot structure catches up with years of being shod.
Phil