Two methods exist, method one uses the AT.EXE command and method two uses the Scheduled Tasks utility located under the My Computer icon on the server.
The AT utility can be used to schedule backups from the CMD prompt by placing your backup command into a cmd file eg svrback.cmd and the scheduling it to run at say 10pm everynight. The following command will do the trick.
AT 22:00 every:M,T,W,Th,F c:\svrback.cmd /interactive
Alternately you can place your backup script into a cmd file eg svrback.cmd and then follow the add task wizard from the Scheduled Tasks icon within the My Computer icon on the desktop.