What would be really interesting to see is a series of identical shots, 1 every hour (or similar) to show the different light effects through the day - what you've posted is on the way towards that - I realise that this might be a bit impractical because of the length of time required to stay in one spot when it's not night-time

Yes, I thought of that too late! A set taken during an hour or so over sunrise would work well. I did try cropping these to be the same frame, but none were then as satisfactory.