I'm getting duplicated rows when table relationships are established...

hi, PatrickLamoste 

Since your two table is a many to many relationship, and there is no [DEPARTMENT] filed in table1, so it will lead to this result.

And from your sample data, I think this your expected output.

Create a measure instead of drag [Hours] into visual directly.

Measure = 
CALCULATE (
    SUM ( Table1[HOURS] ),
    FILTER (
        Table1,
        Table1[ENTRY DATE] >= MIN ( Table2[EFFECTIVE DATE] )
            && Table1[ENTRY DATE]
                <= IF (
                    MAX ( Table2[END DATE] ) = BLANK (),
                    DATE ( 9999, 12, 31 ),
                    MAX ( Table2[END DATE] )
                )
    )
)

 Result:

and here is sample pbix file, please try it.

Best Regards,

Lin