I'm pretty unsure how this thing works, is it that I need to hack the same portal for x days, or do I need to hack any portal for x days?
Niantic have confirmed this for us.
You may hack any Portal - it does not have to be the same Portal every time.
It seems it's any portal.
I'm at 10 days at the moment, and on weekends I'm not following my usual daily routine, meaning I'm only walking to a closer portal not en route to work. Still counting.