A timer in PowerShell controlled through a "tick" event instead of a start-sleep. Script can be run standalone out of the box.

timer.ps1

<#

Good example inspired from here
https://gist.github.com/SteveGilham/98a39f621cfed70bfa0a

To explore possible events, type in 

$timer | gm

#>

#Write-Host "Press any key to continue..."
$Host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown")

# Unregister all events
Get-EventSubscriber -Force | Unregister-Event -Force

# Create a timer object with a specific interval and a starttime
$timer = New-Object -Type Timers.Timer
$timer.Interval  = 1000 # milliseconds, the interval defines how often the event gets fired
$startTime = Get-Date

# Register an event for every passed interval
Register-ObjectEvent -InputObject $timer  -EventName Elapsed  -SourceIdentifier "Timer.Elapsed" -MessageData $startTime -Action {
    
    # Input variables and objects    
    $currentStart = $Event.MessageData
    $timer = $Sender

    # Calculate current timespan
    $timeSpan = New-TimeSpan -Start $currentStart -End ( Get-Date )

    # Output the results to console
    Write-Host -NoNewLine "`r$( $timeSpan.Seconds )"
    #[System.Console]::Write($timeSpan.Seconds)

} | Out-Null

# Start the timer
$timer.Start()

# Stop the time manually
#$timer.Stop()

<#
#-----------------------------------------------
# Keep this process open forever
#-----------------------------------------------

# Just loop forever

while ($true){
  Start-Sleep -Seconds 1
}
#>


#-----------------------------------------------
# Keep the process open for a specific amount of time
#-----------------------------------------------

# Registers an Event, that has a timeout
# When timeout is reached, then the timer gets disposed
# and the events get unregistered

Register-ObjectEvent -InputObject $timer -EventName Disposed -SourceIdentifier "Timer.Disposed"

# Wait until timout or timer disposed by another process
if (-not (Wait-Event "Timer.Disposed" -Timeout 10 )) {
    Write-Host "`nTimeout"
    $timer.Stop()
    $timer.Dispose()
} else {
    Write-Host "`nDone"
}

# Wait another 5 seconds to see the message
Start-Sleep -Seconds 5

# Tidy event registrations and event queue
# The Elapsed events are spent in the handler
# but the one we wait on must be explicitly cleared
Remove-Event "Timer.Disposed"
Unregister-Event "Timer.Elapsed"
Unregister-Event "Timer.Disposed"