As I said earlier this month, this months releases were going to be some short stories. The volume 11 SS happens before the events of volume 9. I would set it to sometime during the month and a half that Sweet covers. Anyways it does a fairly decent job of setting the stage for volume 11’s prologue. Maria takes center stage and is pretty funny with how enthused she is.
Regarding the volume 12 SS If you read the series in order then I wouldn’t read it since it’s kinda spoiler heavy. If the bromance of Basara and Lars is your OTP then you might enjoy it, because the banter between the two of them is always great. Especially considering how Lars is a realist and knows that harems usually never work as out well.