Input required: building finish-to-start dependancy between 2 target sensors

[ragg987]

Hi, I may be approaching this the wrong way so would appreciate any steer or input.

How can I build a finsh-to-start dependancy on target sensors? By which I mean the start start time of sensor 2 is linked to the end time of sensor 1?

Use-case:
My heat pump heats water and provides space heating. Only one can occur at a time, and I have configured the heat pump so that the water heating takes priority over space heating. During the cheap rate window I want to maximise both - i.e. heat water fully and then space heating. My HP allows both events to start at the same time, in this case heating of space starts on completion of heating of water. However, this is wasteful in that space heating has 2 additional circulation pumps that kick in consuming approx 60-100 W.

Advanced scenario:
Heating the water could take less time than the target sensor - e.g. we consumed less water and so it will heat in 1hr instead of the 2hr window defined in the sensor. How would I make the 2nd sensor recognise that the start time can be advanced by 1hr? Or in a more extreme scenario there is no need to heat water and so I can advance space heating by 2 hours?

The only thing I can think of is an automation that evaluates the attributes on sensor 1 and loops through the "target_times:" to find the planned finish time (last event) then call the actions (service) to update the start time of sensor 2. I understand this conceptually but I'm not sure I could construct the Jinja to perform this.