JonWarby

I had a go with this on just the first timer.  I moved the #250 section under the number section of the config file and changed the elements you suggested above.  
After pushing the code it changes the element to a number value.  It seems to drop the : so for example 00:30 is read as 30.  2:30 is read as 230.  
If I change the values on the sunsynk app I can see those changes come through to Home Assistant.
The number is also editable now so I can type in a new number in the time slot.  Whatever number I enter seems to be ignored and after a few minutes just gets refreshed with the value that it's defined in the app.
I think this is the part of the log that is relevant
[11:46:27][D][number:113]: New number value: 200.000000
[11:46:27][D][modbus.number:061]: Updating register: connected Sensor=SunSynk System Mode Time1 start address=0xFA register count=1 new value=200.00 (val=200.00)
[11:46:27][D][number:012]: 'SunSynk System Mode Time1': Sending state 200.000000
[11:46:28][D][modbus_controller:032]: Modbus command to device=1 register=0xFA countdown=0 no response received - removed from send queue
I assume that it's not happy with the value and not accepting it