Background
As explained in T298250, the Android team wants to offer a sort option for user and article talk pages. The categories to sort should include Date posted and Date updated. However, we can not offer this feature because we don't receive the timestamps/dates from the server.
The Task
Serve up timestamps/dates of talk page edits in the /page/talk endpoint
https://en.wikipedia.org/api/rest_v1/page/talk/Barack_Obama