Yep,
nu på torsdag means exactly that, and there's a similar emphasis of the word
nu in other temporal phrases related to the present.
Ha, your Swedish experiences sound very similar to mine, so I can empathise. I've been here for nearly 8 yrs now and still get that sort of interference

Well, I now feel that that use of
nú might have been embedded enough to allow some flexibility, so
nú for þrym dágum might well have been just the most descriptive option to hand, a default if you like, but there may have been other ways of expressing it either commonly or regionally. By the way, I don't believe that
ymb þæs does actually mean 'ago', I think the OE Thesaurus is wrong to list it as such, and if you discount the OE Thesaurus all sources indicate that it means 'after that'..
But you're right about the dearth of opportunity for instances of phrases like 'ago' in OE writing.