The new key interval=* for adding the departure times interval of a public transport route was recently approved after two weeks of voting.
I have created a new wiki page to document this key:
https://wiki.openstreetmap.org/wiki/Key:interval

Full schedule information, however, is still impossible. I originally proposed using “timetable relations” to add full schedule information to routes. I have since realized that this system would quickly become an out-of-date mess.
I have now simplified the proposal to be easier to add and maintain, while still keeping most of the same information in the database.

The key departures=* is my solution to keeping timetables simple and easy to maintain.

https://wiki.openstreetmap.org/wiki/Proposed_features/Public_transport_schedules/Departures

I would really like people to give feedback to help make this proposal work for everyone. I know that for many bus routes, it would be very difficult to add and maintain full schedule information. Those routes should therefore only be given the tag interval=*. Others, however, including many ferry routes, would be very easy to add schedule information to.

Please use the talk page for giving feedback.

Thanks