A Jupiter day is 10.5 Earth hours, so if we take the definition of 1h = 1/24 of a day, a Jupiter hour would be 10.5 / 24 = 26 min. So 17 Jupiter days fit well inside an Earth day, you got something!
Both of you are kind of right. It's still an insane feat of endurance but averaging an 18 minute mile is pretty damn slow and likely zone 2-3 even in rugged terrain for an athlete like her.
High intensity isn't just a generalized term but specific to heart rate, lactate buildup, and anaerobic states.
Seriously? There is a difference in intensity between 2 marathons over 17 hours, vs 2 marathons over 8 hours. The higher intensity is harder, that's why you get a medal for finishing fast.
Of course it can. You just need to define what you're comparing it against.
Surely two marathons per day is lower intensity than two marathons per half-day or 3 marathons per day.
Compared to the common sport professional performance, I would say. Not many people can do a marathon, less two in the same day, even less two per day during 40 days.