When you share a link out to edit externally a document can you shut down access after a bit?

Yes the end user can create and enable links for external sharing in office 365.  To disable they need to go to the individual document and turn it off manually.
You can also automatically control access with Azure Rights Management to automatically expire access to the document.
This feature is part of the Microsoft Enterprise Mobility Suite which is a recommend add-on, or you can manually change the permissions to stop access.