All good :-)

I think it's difficult to meaure what the equivalent of one exercise is to another because it depends on how fast you naturally tend to run compared to skip - but since you naturally skip fast you are right you might find it pretty intense.

I should mention that most people who train for the marathon won't do the full distance in training before. They'll train up to a bit over 3/4 of the total distance so if you get to the point where you can fully recover from 2.5 hrs wihtout soreness the next day maybe you'll be right for the full 3 hours?

If you do decide to reduce it to 2 hours you could mess around with the training program to reduce the increases to something safer.

Let us know how it's going What's the charity?