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.

The amount of work done and intensity (the rate at which work is done) are two different measurements.

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.