Uber and Lyft scheduled services are only available in select cities. And my understanding is that they neither reserve a specific car/driver nor lock in a specific fare. They just automatically request a car at the specified time the same as you normally would request it yourself, so it's still subject to availability and surge pricing at the time the actual request goes out.
I just priced a ride from work to home in NYC using moovn's website, and the fare for their "lite" service is comparable to Uber/Lyft/Juno (without a surge). But the website says no cars are available right now for any level of their service.