As a couple of the others have said above, I guess it depends on how you'd define a marathon. I typically won't watch more than two movies a day, and even that is quite rare for me. Or else if I'm watching a TV series, I usually don't do more than two-to-four episodes a day. There have been times when I've watched, say, all the Harry Potter or Hobbit movies in short succession, but it's usually no more than one film a day or every other day.
When I was watching all the LBT films for the first time as an adult, I just did an average of one film every few or several days. Watching a whole bunch of them in a single day does sound kinda fun, but I think I'd also find it exhausting.