For anyone else, I had a response from ACF support as follows…
Not really inside ACF, you would just have to add some general javascript to the page to validate.
But if you use the filter acf/save_post you can call any php you want from there, so you could update the page title from there.
http://www.advancedcustomfields.com/resources/actions/acfsave_post/
Have a look at the docs above, hopefully that will get you where you need 🙂
