It is something that comes up often enough. I have no good answer for why. But there is something of a workaround. You can add multiple THEN actions that do nothing different. For example, if you want a fan on for 30min after a button was pushed:
IF Button On THEN Fan On + Fan On (with 5min delay) + Fan On (with 5min delay) + Fan On (with 5min delay) + Fan On (with 5min delay) + Fan On (with 5min delay) + Fan On (with 5min delay) + Fan Off.
Your mileage might vary a bit. I have used it for 10 and 15min "pauses". Yes... I know it is not 5min, but close enough.