The default format for the custom metadata “date” type is “short date”. If a field with the short date format is synced with Aeon Timeline, both century data and time data will be truncated on import to Scrivener. If changes are then made on the Scrivener side unwittingly (e.g., changing the day without realising the century and/or time is missing) and then synced back to Aeon, the data is lost permanently. This is an easy error to make, especially if the user has Aeon create the metadata field.
I suggest changing the default date/time format to one including both century and time, such as “medium + time”, or alternatively permitting the user to select a default date/time format.