For me, it was around 13 hours. It wasn't because of job, or deadline or anything, I just simply spent pretty much the whole day with coding. One day I woke up around 6 am, started coding at 7 am, and I didn't stop until 8 pm. I just felt like doing it, I had so many ideas I wanted to accomplish, and I had nothing else to do the whole day, so I had no reason to stop. Of course I took a few breaks, for example to eat, but they weren't longer than 15 minutes. I have done this a few times actually.
And actually I didn't feel bored or tired of it at all, I enjoyed doing it.
How about you?