Why do you think it's a problem to set the "off" times in the scheduling of each device, I agree that it may seem a little bit tedious......but really does not take more than a few minutes to do my whole house setup of 9 rooms.
I have some rooms set to turn off at different times.......'cos I'm/we're not in all the rooms at the same time.
I forgot to mention that I also control the 'rooms' via Alexa.
I also have set up a 'routine' in Alexa to "Turn off heating"...... This routine does "exactly what it says on the tin" .....to use a Ronseal quote. I also have a routine to turn the heating back on again.
@gazzrenn to turn them off all at once could you just not just set yourself to away mode manually?