I don't think I've done any longer than 10 hours.

Years ago when I used to work in a nightclub I would sometimes work from 6pm-4am, with only two 10 minute breaks. And I'd be on my feet the whole time. My feet used to hurt so bad on the days after work.

I now work a 9-5 job. The latest I've ever left the office is 7pm, when I've been extra busy.