About 0.3 sec for a hundred of files (on my system: amd a10 7800).
Therefore 1 000 000 * 0.3 = 300 000 sec.
I.e., 83.33333... hours.
I.e., 3 days and a half (about).
On a better system, it could be less than that.
I used the following command from an elevated command prompt, when I was already in the test folder: icacls * /grant xilo:F /T /Q