Multiple all-nighters (all day every day):

1) Working, studying and developing an Android game as pet project. Last few weeks before release (yup, I've set a deadline for a pet project) my day consisted of uni, work, more work and 4-5h sleep.

2) Having worked on my thesis (Development of a CPU/SoC + Firmware + Linux kernel) and actual paid work. In parallel. Because, you know, I need to eat and pay rent and shit while I'm writing the thesis. And debts at that moment were not an option (still made some). All-day all-night all-week. After submitting the thesis I went to the doc and enjoyed 2 weeks of doing nothing.

3) Sometimes on my main open-source project after regular work hours. If I have the motivation and ideas that I want to check out or prove it gets late/early too fast.