When doing my PhD, I was working in a research center which was open 24/7. I would go to work at 14, starting with a lunch at the cafeteria. Then hopped to buy some groceries. By 17 a lot of people were gone and I could start to really work through the evening and the night, until about 5 am when the sun was raising - which was the signal to go to bed.

I felt like a vampire, had zero social life but did fantastic work.

The main thing was that I knew it would be temporary and not sustainable, which also made me very happy (it was a fun experience, au from family and friends, and I knew I would be back to normal life soon).