Loop until reg key exists?

.EXE number 1 is called ParentBoot.exe

.EXE number 2 is called RebootUtility.exe

ParentBoot.exe will check for system up time.  If your system has not been rebooted for 'x' number of days it then launches RebootUtility.exe.  RebootUtility.exe prompts the user with a dialog.  This dialog has 2 buttons.  "Reboot Now" & "Delay Reboot for 1 Hour".  (note:  if they never press either one the system will reboot in 5 minutes).   

If the user pressed "Delay Reboot for 1 Hour" I execute this code

$regkeypath = "hklm:\Software\MGH"

$value1 = (Get-ItemProperty $regkeypath).OneHour

If ($value1 -contains '1') { Start-Sleep -m 1 }

ELSE { New-ItemProperty HKLM:\SOFTWARE\MGH -name "OneHour" -Value "1" }

My issue/question stems from ParentBoot.exe.  After it launches RebootUtility.exe it sleeps for 15 seconds to see if they pressed "Delay Reboot for 1 Hour"    But what if they wait 60 seconds?  Or 90 seconds? 

So can PowerShell check for a reg key and if not there Loop until it does find it?   And if it loops for 5 min then the system will reboot anyway. Or the user pressed Reboot Now and then it's all good.

While(key does not exist)

Delay(2)

EndWhile

Something like that but in PowerShell