In a 48 hackathon I coded for 45 of those hours, the other 3 hours was spent sleeping.
I even had a piss jug and drank as little as possible to save time. This was in my younger days......
This was obviously an extreme case, but I can comfortable code for 10 hours a day now but every now and then I code for much much longer when deadlines are tight. Last year I pulled at least 1 all nighter coding session per week which is 15-20 hours coding on their own...