This time I used the Handbrake settings mentioned in https://www.youtube.com/wat...
... to optimize for YouTube. It resulted in no re-encoding it seems, as the video was available before I finished typing this up!
I initially left the camera out in its fully-enclosed case from 2:21am to 3:54am. At that point the battery was almost done, so I took it out of the case and hooked it up to my external battery charger, and let it run again until 6:05am.
(This was all using DST on the night DST stopped, so the times are probably all off by an hour earlier if you're strict about that kind of thing)
This time, instead of resizing the 3000p images down to 2160p, I simply cropped a 2160p section out of the centre of the images.
The images are way to bright, so next time I think I will follow Matthew's lead and use 20s exposures.