On a mac it is possible to get a deeplink, clicking on which one directly opens the ulysses sheet. They look like ulysses://some_path_and_code. Might it be possible to insert these links somewhere in Aeon Timeline, so that one could open the sheet right from the Timeline?
You can add it as a link to an event via the Attachments tab of the inspector (paper clip icon). You will then be able to click on this link in the Inspector to open the sheet from the Timeline.
You can read about links here: Images, Attachments and Links - Aeon Timeline 3 Knowledge Base