@Tetsujin I have another question about your 'alarm' app requirements. More specifically, is the 'spare' iDevice in question always powered up and connected to the internet?

@Monomeeth Yes. Old iPhone 5S, no SIM, but plugged in & wifi'd. BTW, I found one app that says it can do auto-off after x mins... doesn't work, leaves the playlist running. 'My Music Alarm Clock'