New Rachio user here. I encountered this issue and was going to post about it but found this thread. Just to bring you up to speed, I have tried Chrome, Internet Explorer, and Edge browser all using Windows 10 and none of them allow you to select zones when creating a fixed watering schedule of any kind.
You can make the selections on the mobile app and then edit the parameters of the schedule from the browser but you cannot create it from scratch in the browser. Would be nice to see this fixed.