I was able to remove the defaults to nothing, but I obviously changed something so now I can't put anything in.
It's entirely blank ATM but when I put anything in the schedule (like in the pic), it comes up with the error. I've tried a ton of different combos of times and General/Motion/Alarm.
I reset the defaults under all "Storage" as well as under all "Events" then I was able to save "Storage > Schedule" then go back and reset my "Event" timing/schedule.
I had this problem. I think what is wrong for you is that you will only be able to save the schedule if the camera profile configuration is set to "Scheduled". If it is set to "Fulltime", then you can't limit the times for these controls, and certainly not for the General category.