score:6
It depends on which train you're selecting.
For the trains billed as "SJ Snabbtåg" the ticket is usually only valid for a particular train.
However SJ also sells tickets for the local/regional Øresundståg. Tickets for these departing from Copenhagen Airport (and other stations in central Copenhagen) are valid for departures within ±3 hours of the nominal departure time. (https://www.oresundstag.se/information/rese-och-kopvillkor/ in Swedish).