I've been working on a teaching problem. Not a bad problem, but instead a problem with good potential for student learning and growth.
I was inspired to work on this problem today in school, then later at the University class, I was inspired more. So tonight I pulled together all the pieces and made a plan. When I published the plan for colleagues' view, a couple of colleagues took a look at this late hour too. Teachers work all hours of the night.
What we really like is doing well by students, and problems that have potential for good work are a welcome reason to stay up late.