I got an early check in but then I'd paid for the night before anyway. Hotels aren't that expensive, and I think trying to check at that hour for a room booked from that day is a bit cheeky and I think most hotels would decline such a request. It's worth paying for the night for peace of mind. If they won't give you an early check-in - what will you do for a good few hours?

I found visa process (by post) very straightforward, and quick. Just be careful with the photo size - they are very particular and IIRC it's not quite the typical 'passport photo' size.