1. These tweaks require that you venture into your registry, please backup your registry.
2. Go to Start > Run when the Run box opens type in regedit (if that didn't work, try 'regedit.exe' )
3. Your registry should have opened [Just checking...have you backed up your registry?] Navigate to the following keys; HKEY_CURRENT_USER > Control Panel >Desktop
4. On the pane to the right double-click on MenuShowDelay, it should open up a dialog box with a set value (it should be 400), change that value to 10.
5. Click OK, you're done

Souce: Here