TripAdvisor says welcome until 2230 - we are looking to arrive at midnight - is it still possible to stay with you?
I have only stayed there once but it is essentially family run hotel and I do not recall there being night staff as one was given a key to the front door. I would recommend making a prior arrangement with the hotel if you intend to arrive later. They were very helpful as I remember. Maybe this helps.
Get an answer from Hotel Bristol staff and past guests.