Scheduled Actions now include a sys.updatedAt timestamp as well as sys.updatedBy as a Link object, providing a more predictable location for detecting when a change has occurred on a scheduled action.

• The updatedAt field will always be a Zulu (e.g. UTC +00:00) timestamp that will be updated whenever a change has occurred, including the execution of the scheduled action.
• The updatedBy field will show the last user that made a change to the scheduled action, such as creating or canceling an action.

You can learn more about the Scheduled Actions API in the Content Management API documentation