In September the useful part of the blue hour here lasts about twenty minutes. The sky and the street lights balance for maybe eight of them. I now set up half an hour before sunset and take a test frame every two minutes, so the right moment is already framed and focused when it arrives.
White balance: fixed at 4300 K. Auto white balance kept pulling the sky towards grey.
A 6-stop and a 3-stop filter together gave a visible magenta cast on the cheaper glass. Swapping the order made no difference; replacing the 3-stop with a better one fixed it. For exposures longer than two minutes I also cover the viewfinder, otherwise light leaks in from behind.
Around the solstice the sky never gets properly dark. Exposures that would take thirty seconds in October take four. The low, flat light is kind to faces and unkind to anything shiny.