If a marathon game lasts say 650 turns (pretty reasonable for a dominance victory on huge map with around 8-10 AI players I said I average 700 turns but that's generally the max not the average) and you average 2 minutes per turn (I have a fast computer) than that's 1300 minutes for a game which is 20 hours which is less than 24 hours. And yes as I said sometimes I quit when it's obvious I'm going to win and I don't care about getting revenge on the other players (I tend to take out the top two players and then decide if I'm in the mood to go after everyone else). That's pretty much a worst case as in marathon your time between turns is generally pretty fast on a good computer. The first 200-300 turns go quite fast, one down side of marathon is there can be a fair amount of clicking on next turn in the early game. Also my pattern is more like play Civ for 4 or 5 days in a row then do other things on the other days, I didn't make that clear so we are talking 4-6 games a week for well...I got Civ5 just as the first expansion was coming out (but didn't probably start doing marathon for a month or two after that), so being conservative say 25 months x 4 x 4=400 games. Or let's see I've got 4391 hours clocked on steam if my average is say 16 hours per game that's still close to 300 games (but that's not a good metric sometimes I play off line --thanks ISP---sometimes I accidently leave Civ running and I have no real idea what my average game time is I'd have to say I probably quit early maybe 50% of the time or say around turn 400). It's as you see entirely possible, I don't recommend it and it helps being unable to do much else (and going days without sleep or an hour or two is normal for me). And I have a bad tendency when something goes wrong in real life to look for an earlier save file.
I do sometimes think of doing epic, but marathon just beckons me. But of late other things are interesting also (like relearning calculus just for fun). The first game I ever played on a computer was an Ancient Egypt text based 'guide your civilization' game in the 70's...you might say I got hooked then and Civ5 finally gives me my fill of that type of game (though more complex than I ever dreamed of back then).
If someone mods marathon to balance science and a few other things better please let it be known, I'd love to test it. The thing I'd really like is double or triple huge maps as exploration is often my favorite part of the game....though I expect BE to take up a lot of time soon as SciFi is my favorite genre.
One of the best things about Civ5 is how many different ways there are to play it, my big dread is it will somehow be converted to a console and many options will disappear like marathon.
