Import/Direct Query Relationship Error (My date data types are both datetime)

Hello,

I have a relationship between a DateDim table (Import) to a OrderFact table (Direct Query).  

I'm then calculating the amount of time between two dates, excluding weekends.  Calculated column below with error message:

It seems as if there is an issue with the relationship so I went and looked to find this:

I've never seen that type of annotation before for relationships.  Without knowing what the opposing carrots mean, I cannot really figure out a resolution.

In addition, to double check on the relationship, I created a table with all of the date fields, which all worked and lined up correctly.  For some reason, I cannot enact the calculated column though.  I either get the error above, or I get "Calculate is not a function" and that there is no relationshiop between the date columns.

I'm at a total stopping point, any help is appreciated.

Thanks!