Show-InstallationRestartPrompt -countdownSeconds 900 gives the user a 15 minute countdown.
Show-InstallationRestartPrompt -countdownNoHideSeconds 900 only gives the user 60 seconds.
What gives?
Show-InstallationRestartPrompt -Countdownseconds 600 -CountdownNoHideSeconds 60
That CountdownNoHideSeconds is a NO HIDE for the last 60 seconds of the countdown. You could do
Show-InstallationRestartPrompt -Countdownseconds 900 -CountdownNoHideSeconds 900. That will never hide for the user, but might annoy the user.
Hope that makes sense.