You could technically walk a mile in 12 minutes but you would need to walk at a pace of 5 MPH to complete a mile walk in 12 minutes.
For most people walking at a brisk pace it takes the person at least 20 minutes walking at 3 MPH to walk a mile.
So if you want to complete a mile walking you need to speed up you walking pace from 3 MPH to a faster 5 MPH.