When you add a schedule, you can only schedule the group to turn off but not to turn the group on. I‘m aware of the workaround with scenes, but this is a basic functionality. This has also been addressed in an issue on github https://github.com/dresden-elektronik/deconz-rest-plugin/issues/699#issuecomment-487392840
@de_employees can you please react here? I am not going to ping you everytime there is a question for you.
We thought about adding a basic “on” command to this back in the time. But have dismissed this idea in favor of scenes since “on” alone can be confusing without setting a specific brightness. Scenes are more work to setup but provide full control over on/off brightness and color.