Arriving off a flight from Edinburgh (both which currently arrive into terminal 5), how much time should I allow before aiming to catch a train from Arlanda Central? I have an EU passport and may or may not have checked luggage.
In terminal 5 it depends on what gate you arrive at. The F gates are quite a walk from security. The entrance to Arlanda Central is located in Sky City between Terminal 5 and Terminal 4. I would count on 5-15 minutes to get out of arrivals - then another 10 minutes to get to the station so with some marginal 30 minutes should be fine. With checked luggage it is much harder to tell. Normally luggage appears soonish at Arlanda but it is not possible to be sure about this.
This page claims somewhat shorter walking times.