Fair point, it was. However I just tried again after verifying it is in normal mode and Do Not Disturb is disabled. Same result. While locked, with screen off, the “speak text” part of the alert did not happen yet there was an alert displayed when later waking the phone which implied the time-based trigger fired and the workflow was executed. So sadly this appears to not function as a time-based “speak message” alert like was wanted. It may work for other actions, such as time-based HomeKit actions to blink the lights, but “speak text” at least does nothing while the phone is locked with screen off.
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matigo.ca.