Launchd running an Applescript every two hours
Isn't StartInterval the key for running periodically? In your case, set to 7200 (seconds)?

https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html#//apple_ref/doc/uid/10000172i-SW7-SW7