When writing my bachelors thesis i worked five weeks 16-17 hrs a day without taking a single day off.

I didn't repeat this when doing masters.

I think I ate most of the time in front of some papers.

But I did interpret the questions a little bit differently maybe: of how long I worked without real break (a weekend or at least half day off really doing something else then woking or fulfilling very basic needs), and that wouled be the five weeks.

If the question is how long did you work without leaving your desk to pee or whatever I would not the 3h!