Thanks all!
There are many obvious traps in defining how much walking counts that would immediately start fistfights, even in civilized company 
Of course, this isn’t a hypothetical question…
Someone is in the midst of a “most consecutive days to **run **a marathon” effort, not a “most consecutive days to complete a marathon distance” effort, and does an awful lot of walking, and a lot of them are 8/9+hr runs.
Does this personally offend me? No, not at all. Am I curious as to whether having some days where you’ve walked most of it would be ratified by Guinness or other record-keeping body…yes, yes I am.
I was following someone on Strava doing just this - most consecutive days of ‘running’ a marathon and supposedly ratified by Guinness. They clearly had the fitness as there were some (occasional) fast (3’30"ish) times in there, but (for me) there were too many days of 9-10 hour marathons, with lots of walking and lots of breaks (45min/km). I have no issue with walking the odd km, but the regular long breaks made me give up following them. I do feel the 6-7 hour cutoff seems about right.