identify overlapping entries

SebastianAlmer 

If you wish to use Direct Query, you can (NB, I've added another overlapping row to date 2/03/2021 to check if all overlapping rows are returned) :

1) Create the DateTime columns in the table using calculated columns with:

StartTime = TableDQ[date] & " " & TableDQ[start_hour] & ":" & TableDQ[start_minute]

And the equivalent for the EndTime column.  Set the Data type to Date/time:

2) Create a measure to establish the row order by date/employee/task:

Sum StartTime = SUM(TableDQ[StartTime])

Order by date =
RANKX (
    FILTER (
        ALLEXCEPT ( TableDQ, TableDQ[employee], TableDQ[date], TableDQ[Task] ),
        NOT ( ISBLANK ( [Sum StartTime] ) )
    ),
    [Sum StartTime],
    ,
    ASC
)

This gives you the following table visual:

3) Next create measures to establish the StartDateTime and EndDateTime for the comparison:

StartDateTime =
VAR starttime =
    MAX ( TableDQ[StartTime] )
RETURN
    CALCULATE (
        starttime,
        ALLEXCEPT ( 'TableDQ', 'TableDQ'[date], 'TableDQ'[employee], 'TableDQ'[Task] )
    )

EndDateTime =
VAR PrevPeriod = [Order by date] - 1
RETURN
    CALCULATE (
        MAX ( TableDQ[EndTime] ),
        FILTER (
            ALLEXCEPT ( TableDQ, 'TableDQ'[date], 'TableDQ'[employee], TableDQ[Task] ),
            [Order by date] = PrevPeriod
        )
    )

4) and finally the measure to identify the rows which overlap:

Indentify overlapping DQ =
VAR SelPeriod =
    CALCULATE (
        [Order by date],
        FILTER ( TableDQ, NOT ( ISBLANK ( [EndDateTime] ) ) )
    )
VAR _table =
    CALCULATETABLE (
        VALUES ( TableDQ[date] ),
        FILTER (
            TableDQ,
            [Order by date] >= SelPeriod - 1
                && [Order by date] <= SelPeriod
        )
    )
VAR _date =
    CALCULATETABLE (
        VALUES ( 'TableDQ'[date] ),
        FILTER ( ALL ( TableDQ ), [StartDateTime] < [EndDateTime] )
    )
RETURN
    COUNTROWS ( INTERSECT ( _table, _date ) )

And you will get this: