I loved this too. Very reminiscent of the BBC's notorious Ghostwatch, but excellent in it's own right too. It nails the look and feel of the 1970s TV talk shows, and is also genuinely scary. Oh, and we need more films with David Dastmalchian in the lead.

My review here (if you're interested):

Film Review — Late Night with the Devil | Simon Dillon Cinema (medium.com)