However, saving the expression as a dashboard panel worked fine, and they then appear under the 'Visualizations' section of the Management/Saved Objects tab. This works, as it means all my searches, visualizations (including Timelion) and dashboards can be imported/exported in one go, and I can get back to the original tlion query by looking at the saved panel expression.
I guess if I had one final comment, it might be a good enhancement in the future if the "Save entire Timelion sheet" option in Timelion made the sheet available within the Saved Objects/Visualizations area too as at the moment it's a little confusing that you save it, but it would not be present on an export so would be lost if you then re-imported the objects into a new Kibana instance (as I did).
Thanks again for the rapid (and v. useful) advice,
One thing that might be throwing you off on your search for the timelion saved object, is that the id of a saved object used to be the title of the saved object but with spaces replaced by underscores. If your title is actually tlion esb ins AFB MaxProcessing CreateOffer then you would use that in your search instead of the former id string with underscores.
I'll discuss with Timelion developers and see if it makes sense to add them as another object type to export. And if so, I'll file an issue to get it in the queue.