Could be done by taking the train from Lund C at c. 10:39 but that means too little room for disruptions if needing to make the 60 minute check-in cut-off in-person at CPH. Not the relaxing way to do that, especially since passport control and security screening at the airport take time too. In economy class on SAS to IAD, it’s general security screening unless having SAS*G status. Plus and Business class on SAS get SAS fast Track security screening access, but only at the SAS dedicated checkpoint — which is to the left (on the Burger King side) when going upstairs above the check-in level.

Don’t plan based on latest train departures from Lund. Plan based on what happens if there is a train schedule disruption and needing to hit the road by car/bus to at least Malmö-Hyllie and then take a train and/or bus to CPH from Malmö-Hyllie.

9:39 train departure form Lund C by train would be what I would do nowadays were Lund to CPH be relevant to me like it used to be. 9:19am train departure is even safer. I would definitely not leave Lund C before 8:59 for a May 18th flight to IAD. You can buy and activate the train ticket on the Skanetrafiken app on the phone on the day of travel from Lund to CPH — once it’s activated on the day of travel, the ticket remains active for the whole day on the phone even if without internet connectivity. That way you don’t need to worry about buying the train tickets at the station and losing time there.