Upon a quick look, I couldn’t find a regulation regarding that time limit on the Swedish Finansinspektionen’s website, but I assume it is the day following the trades. At least the short-selling rocket following the interim report was dated in the register as the report day, but was reported the following day. Therefore, the T+2 settlement cycle time limit for stock trades does not seem to apply to short selling.
Unlike the Finnish short register, the data in the Swedish register is updated automatically once the notification has been made to them. As a result, the register data can be updated multiple times a day, and the final situation on September 9th was 6.06%, differing from the 6.17% situation I linked above. In Finland, the short register data is updated once a day, and positions below 0.5% are not reported at all. In Sweden, only positions below 0.1% remain under the radar.