I tracked what I spent my time on for the whole of last year (you can read about this more here), as I finished university and started my PhD. I've always thought that I was working a lot since my course was quite intense, but I found out that on average, I also work around 5-6h per day. To quote the post: 

Finding out how little focused work I do, even on the days that feel productive, was one of the biggest surprises of analysing my data. It turns out that a typical working day (9-17) would usually only give around 5-6 hours of actual work, while the rest of the time would dissolve on low-focus work, chatting to people, coffee breaks and other little distractions. While there were days when I would reach 8 hours of focused work (for focused uni work I had 32 such days this year), they required either spending the whole day (9-22) working or a lot of effort to stay focused. Both were quite tiring and unsustainable in the long run.

For this year, my average number of working hours per week is 33 (this doesn't exclude free days/holidays though).  There is quite a lot of variance, with my last 5 weeks of working hours being: 58, 31, 29, 50, 39. It seems like there are weeks of high intensity (usually caused by a surge of motivation, coding-heavy tasks or an upcoming presentation), followed by weeks of lower motivation & ability to focus. It's interesting that it still averages out to ca 6h/(working) day.