I have managed to solve my problem partially, thanks to bluntTony, as he provided me with a script that allows me to schedule a Shutdown task at a particular time to be executed and shut down the client PCs.
the the problem that Im facing now is that if I schedule it like that it will shut down the PC directly without any warning for the user, and if by chance an employee is still working late at the office and it comes to the time that it is scheduled for the PC to be turned off, it will shut down and all his work will be lost.
I have attached the VB code provided by bluntTony and what Im looking for now is a way to warn the user 15 min before the shutdown action, and allow him to Cancel it when needed.
Set objShell = CreateObject("Wscript.Shell")
set objWMI = GetObject("winmgmts:\\.\root\cimv2")
set colScheduledJobs = objWMI.ExecQuery("Select * from Win32_ScheduledJob")
For each objJob in colScheduledJobs
If InStr(UCase(objJob.command),"SHUTDOWN") > 0 Then booFound = True
If Not booFound Then objShell.Run("%systemroot%\system32\at 19:00 shutdown.exe -s -f -t 30")