Timer in WPF Label anzeigen

[xml]$Timer_Form = @"  

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  

                Title="Computer Reboot Notifcation" Icon="C:\Users\fritz\source\repos\WpfApp1\Warnung.png" Height="446" Width="725" ResizeMode="NoResize" Topmost="True" WindowStartupLocation="CenterScreen" Background="White" FontFamily="Arial Black" ShowInTaskbar="False" SizeToContent="WidthAndHeight">  
    <Grid Margin="15,15,15,15">  
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <Label Content="Nach der Installation von Sicherheitsupdates ist ein Neustart des Computers zwingend erforderlich.&#xD;&#xA;Dieser ist auch nach mehreren Hinweisen nicht erfolgt.&#xD;&#xA;Zur Wahrung der Sicherheitsniveuas muss dieser Heute erfolgen.&#xD;&#xA;Sie haben nun noch einmalig die Möglichkeit den Restart zu verschieben.&#xD;&#xA;Ansonsten sichern Sie Ihre Daten, schließen die geöffneten Anwendungen &#xD;&#xA;und klicken anschließend auf den Button Neustart.&#xD;&#xA;&#xD;&#xA;WARNUNG: Der Rechner wird nach Ablauf der Zeit neu gestartet!&#xD;&#xA;&#xD;&#xA;Vielen Dank ihr IT-Services-Team" FontFamily="Arial" FontWeight="Bold" FontSize="14" Padding="10,10,10,10" RenderTransformOrigin="0.5,0.5" Margin="0,0,0,200">  
            <Label.RenderTransform>
                <TransformGroup>
                    <ScaleTransform/>
                    <SkewTransform AngleX="0"/>  
                    <RotateTransform/>
                    <TranslateTransform X="0"/>  
                </TransformGroup>
            </Label.RenderTransform>
        </Label>
        <Label x:Name="LabelTimer" Content="LabelTimer" HorizontalAlignment="Left" Margin="0,190,0,0" VerticalAlignment="Top" Height="56" Width="340" FontFamily="Arial Black" FontWeight="Bold" FontSize="40" Foreground="Red"/>  
        <Grid Margin="10,270,10,0">  
            <Button x:Name="B_Reboot" Content="Neustart" HorizontalAlignment="Left" Margin="0,20,0,0" VerticalAlignment="Top" RenderTransformOrigin="0.393,0.489" Width="120" Height="50" FontFamily="Arial" FontWeight="Bold"/>  
            <Button x:Name="B_1Hour" Content="1 Stunde&#xD;&#xA;verzögern" HorizontalAlignment="Left" Margin="140,20,0,0" VerticalAlignment="Top" Width="120" Height="50" FontFamily="Arial" FontWeight="Bold"/>  
            <Button x:Name="B_4hour" Content="4 Stunden&#xD;&#xA;verzögern" HorizontalAlignment="Left" Margin="280,20,0,0" VerticalAlignment="Top" Width="120" Height="50" FontFamily="Arial" FontWeight="Bold"/>  
            <Image HorizontalAlignment="Left" Height="99" VerticalAlignment="Top" Width="120" Margin="545,0,0,0" Source="C:\Users\fritz\source\repos\WpfApp1\IS_Logo.bmp" Stretch="Fill"/>  
        </Grid>
        <Grid Margin="-1030,0,1030,133"/>  
    </Grid>

</Window>
"@  

#Timer



#Create a form
$XMLReader = (New-Object System.Xml.XmlNodeReader $Timer_Form)
$TimerForm = [Windows.Markup.XamlReader]::Load($XMLReader)

#Reboot Button
$B_Reboot = $TimerForm.FindName('B_Reboot')  
$B_Reboot.add_click({write-host ich habe es geschafft,$TimerForm.Close()})

#1Hour Button
$B_1Hour = $TimerForm.FindName('B_1Hour')  
$B_1Hour.add_click({      
      $timerUpdate.Stop()
      $TotalTime = 3600
      Create-GetSchedTime -SchedTime $TotalTime
      $timerUpdate.add_Tick($timerUpdate_Tick)
      $timerUpdate.Start()
      $B_1Hour.IsEnabled = $false
      $B_4Hour.IsEnabled = $false
})

#4Hour Button
$B_4hour = $TimerForm.FindName('B_4hour')  
$B_4hour.add_click({
      $timerUpdate.Stop()
      $TotalTime = 14400
      Create-GetSchedTime -SchedTime $TotalTime
      $timerUpdate.add_Tick($timerUpdate_Tick)
      $timerUpdate.Start()
      $B_1Hour.IsEnabled = $false
      $B_4Hour.IsEnabled = $false
      })

#Function für Timer
Function Create-GetSchedTime {   
Param(   
$SchedTime   
)
      $script:StartTime = (Get-Date).AddSeconds($TotalTime)
      $RestartDate = ((get-date).AddSeconds($TotalTime)).AddMinutes(-5)
      $RDate = (Get-Date $RestartDate -f 'dd.MM.yyyy') -replace "\.","/"      # 16/03/2016  
      $RTime = Get-Date $RestartDate -f 'HH:mm'                                    # 09:31  
      #&schtasks /delete /tn "Post Maintenance Restart" /f 
      #&schtasks /create /sc once /tn "Post Maintenance Restart" /tr "'C:\Windows\system32\cmd.exe' /c shutdown -r -f -t 300" /SD $RDate /ST $RTime /f 
}

#Function Timer-Formular 
Function timer-form
{
[System.Reflection.Assembly]::LoadWithPartialName("System.Windows.Forms") | Out-Null  
[System.Reflection.Assembly]::LoadWithPartialName( "Microsoft.VisualBasic") | Out-Null  

$outlook = @(Get-Process | ?{ $_.Name -eq "outlook" }).Count  
$word = @(Get-Process | ?{ $_.Name -eq "winword" }).Count  
$excel = @(Get-Process | ?{ $_.Name -eq "excel" }).Count  

$timerUpdate = New-Object 'System.Windows.Forms.Timer'  
$TotalTime = 14400 #in seconds
Create-GetSchedTime -SchedTime $TotalTime
$timerUpdate_Tick={
      # Define countdown timer
      [TimeSpan]$span = $script:StartTime - (Get-Date)
      # Update the display
      $hours = "{0:00}" -f $span.Hours  
      $mins = "{0:00}" -f $span.Minutes  
      $secs = "{0:00}" -f $span.Seconds  
      $labelTime.Text = "{0}:{1}:{2}" -f $hours, $mins, $secs  
      $timerUpdate.Start()
      if ($span.TotalSeconds -le 0)
      {
            $timerUpdate.Stop()
            shutdown -r -f /t 0
            Remove-Variable * -ErrorAction SilentlyContinue
            Remove-Item -Path "C:\Boottime" -Force -Recurse  
            $global:Form.Close() 
      }
}
$Form_StoreValues_Closing=
      {
            #Store the control values
      }

$Form_Cleanup_FormClosed=
      {
            #Remove all event handlers from the controls
            try
            {
                  $Form.remove_Load($Form_Load)
                  $timerUpdate.remove_Tick($timerUpdate_Tick)
                  #$Form.remove_Load($Form_StateCorrection_Load)
                  $Form.remove_Closing($Form_StoreValues_Closing)
                  $Form.remove_FormClosed($Form_Cleanup_FormClosed)
            }
            catch [Exception]
            { }
      }