The four hour rule caught me by surprise last month at SEA. I needed to check my bag with large liquids inside and planned to work for several hours in the Lounge. The F checkin agent said I needed to wait about 10 minutes until I could check my bag… but that worked out to four hours before the boarding time. I stood off to the side and after about 10-15 minutes, the same agent called me over and said it was fine to check my bag. As soon as she scanned my boarding pass, there was a problem. It was still outside the four hour flight time, but she did override it and checked my bag. So it’s definitely possible, but YMMV.