Since you want to configure the same time zone for all, depending on the DEM version (version 2006 and higher), you will be able to configure the time zone system based using a Startup Task (Computer Environment tab) and utilizing PowerShell's cmdlet Set-TimeZone (https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.management/set-timezone?view=powershell-6).
This way you are managing the setting from DEM instead of using a computer-based GPO. By configuring it on a computer level using a Startup Task, you are not bothering the user during or after logon.
