4h 40m in midwinter, 20h 20m in midsummer :D (plus nearly permanent twilight) - i suppose that might work if i was a bear that hibernates (and i believe the bears are right about this).
That is too soon. I would go to sleep before kids come back from after school activities. Most of the colleagues would still be at work when I go to sleep too.
The sun won't be affected by what you set your clock to. If you want to optimize your schedule for sun exposure, you can do so. You can even travel twice a year near the poles to get sun all day everyday. Or no sun ever, if that's your jam.
Around here, that would be pretty much hibernation.
...so go to sleep while I'm still at the office at 4:30pm?