Forgot to tell I have Shelly 1 Pro. I had original 0.12.0 but now I have that new firmware. Just it does not help. Some more testing...
finally these work ok and switch delay on/off:)
http://192.168.68.xxx/rpc/Schedule.Create?timespec="0 18 0 * * MON"&calls=[{"method":"Switch.Set","params":{"id":0,"on":true}}]
http://192.168.68.xxx/rpc/Schedule.Create?timespec="0 19 0 * * MON"&calls=[{"method":"Switch.Set","params":{"id":0,"on":false}}]
So create command is just wrong in instructions. Need to check that update command later. But I think it is not obligatory for me.
I can delete all schedules and create on+off schedule every day when new prices available. Better to clean off old schedules anyway.