Crossfilter through three different tables.

To exclude holidays and sick days from the WorkPlanEntry table, you can modify your measure to filter out entries with Title values indicating holidays or sick days. Here's how you can adjust your Time measure:

Revised DAX Measure:

Time =
VAR _filteredDates =
    CALCULATETABLE (
        'Future',
        NOT (
            CONTAINSSTRING ( RELATED ( WorkPlanEntry[Title] ), "Holiday" )
                || CONTAINSSTRING ( RELATED ( WorkPlanEntry[Title] ), "Sick" )
        )
    )
VAR _countMonday =
    CALCULATE ( COUNTROWS ( _filteredDates ), WEEKDAY ( Future[Date], 2 ) = 1 )
VAR _countTuesday =
    CALCULATE ( COUNTROWS ( _filteredDates ), WEEKDAY ( Future[Date], 2 ) = 2 ) 
VAR _countWednesday =
    CALCULATE ( COUNTROWS ( _filteredDates ), WEEKDAY ( Future[Date], 2 ) = 3 ) 
VAR _countThursday =
    CALCULATE ( COUNTROWS ( _filteredDates ), WEEKDAY ( Future[Date], 2 ) = 4 ) 
VAR _countFriday =
    CALCULATE ( COUNTROWS ( _filteredDates ), WEEKDAY ( Future[Date], 2 ) = 5 ) 
VAR _totalMonday =
    SUM ( 'User'[Monday] ) * _countMonday
VAR _totalTuesday =
    SUM ( 'User'[Tuesday] ) * _countTuesday
VAR _totalWednesday =
    SUM ( 'User'[Wendsday] ) * _countWednesday
VAR _totalThursday =
    SUM ( 'User'[Thursday] ) * _countThursday
VAR _totalFriday =
    SUM ( 'User'[Friday] ) * _countFriday
RETURN
    _totalMonday + _totalTuesday + _totalWednesday + _totalThursday + _totalFriday