The main problem in academia is that worldwide those who work a 40 hour week seem to be far less common than those who work, or claim loudly to work, more than 100 (particularly at the earlier career points). I'm lucky enough to have gone beyond the point where I sleep in the lab, but I definitely have done so.

The OP should be able to do a doctorate part time, and in Europe that is definitely doable. The funding and the practicalities are very much subject specific, but it does take a long time -- and is very much a labour of love.