Distinct CountX?

Ok I actually got it figured out, and it was a LOT easier than I thought it should have been 😄

First, I got rid of the relations between the tables.

Then it was just a matter of creating the following measure:

Measure = 

VAR StartDato =
    MIN ( Dato[Dato] )
VAR SlutDato =
    MAX ( Dato[Dato] )

RETURN
    CALCULATE (
        DISTINCTCOUNT('nexus2 Fact_VisiteretTid'[CPRnrKort]),
        FILTER ( 'nexus2 Fact_VisiteretTid', ( 'nexus2 Fact_VisiteretTid'[Start] <= SlutDato && 'nexus2 Fact_VisiteretTid'[Stop] >= StartDato ) )
    )

Seriously, it solved all my problems, and the result validates. Go figure XD