How do package authors find the time?

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Yes, we really work crazy hours (not only) in evenings and weekends (where other academics would spend time on something else than their science, too). It's our hobby. Other people just have different ones.

Many packages got initially created because I needed them for my thesis, like svn-multi, tikz-timing and standalone. On the other hand if I would work 100% of the time on my research and thesis I would be crazy already.

I class my own modest contributions as structured procrastination. I also count my time on this site that way.