There is no option in uber api documentation to schedule rides for future.
But the following products provide Uber pre-booking:
https://www.ridesharp.co/
https://www.trykommen.com/
How is this possible?
They are just providing their own mechanism to 'schedule' a ride. All they are doing is storing the time & details for the request and then making the request call at the appointed time. There is no scheduled ride API.