HOWTO: Calculate Elapsed Business Hours Using PowerShell

# Calculate the number of business hours elapsed since a specified date
# Business Hours; Calculate; Working Hours; Working Days; Holidays

Function Get-WorkingDays
{
    Param 
    (
        [Parameter(Position=0,Mandatory=$True)]
        [DateTime]$Startdate,
        [Parameter(Position=1,Mandatory=$False)]
        [DateTime]$Enddate
    )
    
    $StartHour = 8
    $FinishHour = 17

    # Enter whatever dates here you do not want to be included as part of your business days/hours calculation
    $holidays = @(
        (Get-Date -Date '2018-12-24')            # Labour Day
        (Get-Date -Date '2018-12-25')            # Thanksgiving
        (Get-Date -Date '2018-12-26')            # Christmas Holidays
        (Get-Date -Date '2018-12-27')            # Christmas Holidays
        (Get-Date -Date '2018-12-28')            # Christmas Holidays
        (Get-Date -Date '2018-12-29')            # Christmas Holidays
        (Get-Date -Date '2018-12-30')            # Christmas Holidays
        (Get-Date -Date '2018-12-31')            # Christmas Holidays
        (Get-Date -Date '2019-01-01')            # Christmas Holidays
        (Get-Date -Date '2019-02-18')            # Family Day
        (Get-Date -Date '2019-04-19')            # Good Friday
        (Get-Date -Date '2019-05-20')            # Victoria Day
        (Get-Date -Date '2019-07-01')            # Canada Day
        (Get-Date -Date '2019-08-05')            # Civic Holiday
        (Get-Date -Date '2019-09-02')            # Labour Day
        (Get-Date -Date '2019-10-14')            # Thanksgiving
        (Get-Date -Date '2019-12-25')            # Christmas Holidays
        (Get-Date -Date '2019-12-26')            # Christmas Holidays
        (Get-Date -Date '2019-12-27')            # Christmas Holidays
        (Get-Date -Date '2019-12-28')            # Christmas Holidays
        (Get-Date -Date '2019-12-29')            # Christmas Holidays
        (Get-Date -Date '2019-12-30')            # Christmas Holidays
        (Get-Date -Date '2019-12-31')            # Christmas Holidays
        (Get-Date -Date '2019-01-01')            # Christmas Holidays
    )

    # If both a startdate and an enddate are provided, return the number of business days between the two
    if($Enddate)
    {
        $difference = New-TimeSpan -Start $startdate -End $enddate
        $days = [Math]::Ceiling($difference.TotalDays)

        $workdays = (1..$days) | ForEach-Object {
            $startdate
            $startdate = $startdate.AddDays(1)
        } | Where { $_.DayOfWeek -gt 0 -and $_.DayOfWeek -lt 6 -and $Holidays -notcontains $_.date } | Measure-Object | Select-Object -ExpandProperty Count

        return $Workdays
    } 
    
    # If an enddate is not provided return if the start date is within working hours or not
    else
    {
        $DayStatus = $startdate | Where { 
            $_.DayOfWeek -gt 0 -and # Not Sunday
            $_.DayOfWeek -lt 6 -and  # Not Saturday
            $Holidays -notcontains $_.date -and 
            $startdate.hour -ge $StartHour -and 
            $startdate.hour -lt $FinishHour 
        } | Measure-Object | Select -ExpandProperty Count
    
        if($DayStatus -eq 1) { $true} else {$false}
    }
}

Function Get-BusinessHoursElapsed([datetime]$CompareDate, [switch]$ReturnString )
{
    # Define when you want to start and end the day using military time
    [datetime]$StartofDay = '8:00:00'
    [datetime]$EndofDay = '17:00:00'

    $Now = Get-Date "1/4/2019 13:41:56"

    # If the specified date falls within working hours, add up the total amount of time elapsed since the day begin and subtract the time from the end of the day that hasn't elapsed yet
    if((Get-WorkingDays $CompareDate)) { $ElapsedTime = ($EndofDay.TimeOfDay - $CompareDate.TimeOfDay) }
    if((Get-WorkingDays $Now)) { $ElapsedTime = $ElapsedTime + ($Now.TimeOfDay - $StartofDay.TimeOfDay) }

    # Get the total number of working days between the specified date and now and add 8 hours for each working day to our total
    $WorkingDays = Get-WorkingDays $CompareDate $Now
    $InBetweenHours = (($WorkingDays) - 1) * 8
    $ElapsedTime = $ElapsedTime.add((New-TimeSpan -Hours $InBetweenHours))


    # Format the output so that it looks like an elapsed time including leading zeros where required
    if($ReturnString)
    {
        # We want our final output to include only hours.  We do NOT want it to show days if it goes past 24 hours which is the default behavior so we'll convert any days into hours
        $Hours = (($ElapsedTime.Days * 24) + $ElapsedTime.hours)

        $Hours = $Hours.tostring("00")
        $Minutes = $($ElapsedTime.Minutes).tostring("00")
        $Seconds = $($ElapsedTime.Seconds).tostring("00")
        $ElapsedTime = "$Hours`:$Minutes`:$Seconds"
        
        return $ElapsedTime
    }
    else
    {
        return $ElapsedTime
    }
    
}

Get-BusinessHoursElapsed (Get-Date "12/21/2018 14:43:11") -ReturnString