Hi. I would like to see if / when the valve for my heating system opens and how much in Domoticz.

The valve is this:
https://belimo.ch/pdf/e/SR24A-SR_datasheet_en-gb.pdf
Temperature regulator is this:
https://bevent-rasch.com/wp-content/uploads/TR24-M_datasheet.pdf

How can I get the control signal ...

Great!!

Yes, Domoticz need some calendar where you can put some trigger to start for example a electric heater to the car.
I made a simple script to my car to start the engine heater, and I work monday to friday so this is simple.
Audi engine heater.jpg

But my wife has irregular working hours ...