SoundMachine schedules show up as a source in Sonos, so you can start playback on them. Our service cannot start playback on a third party device, but once playback has been started, our schedule will automatically pick the correct music.
Sonos does offer an "alarm" system, which is like an alarm clock. It can be programmed to start a schedule (maybe at the beginning of the day), and then schedule can run its course. The schedule can even stop music at the end of the day, and then the alarm starts it again the following day. We use it in the office here, and it works very well overall.
Since it is streaming, if the internet ever goes down, you will have to start playback again, by selecting it from the Sonos app.