Using Lingo version 2.1.1 I am able to use a GUI to create a plist file to allow something to run at a specified time on a Mac. I tested this on Mac OS 10.8.4 to great a plist file to run at startup to set the screen resolution with cscreen. It worked great. You do have to lower the security preferences to allow applications from anywhere to allow Lingo to run. There is a newer version of this available from the app store which my be worth the money …
With FileEventer I can watch where the plist file gets saved. In my case test, setting screen resolution with the application cscreen at boot time, the plist file was saved to:
/Library/LaunchDeamons
I was then able to copy the saved plist file to other macs.
See the longish blog posting on this at: