but i suspect its highly inefficient,
This sending an order to the thermostat every 15minutes will empty the thermostat batteries, and create unecessary signals.
Is there something else i could put in the “when” that would make the flow more streamlined?
“This flow is started” is probably not okay as its for manual triggering only?
“the time is 07h30” would probably trigger it only once a day while the flow needs to be triggered twice a day
The solution of @Martin_Tschanun will work fine.
After this optimization you will probably find the need to optimize more:
How about weekends? Same time?
So to make it future proof and understandable, split it up:
Make separate flows for setting the temperature (like Martin proposed) but start them with “when this flow is started” or a virtual device.
And create two flows started by the times, these will trigger the flows create above.
Advantage: when you decide to have a different weekend routine, just add another flow with the desired day and time (and exclude that day and time from the other flow)
And you are futureproof: even if you have a different time for every day. If you want to change the desired temp to 21c, you only need to change just one flow.