what time will it be 1 hour 40 minutes after 20:40 AM?
When you use 24 hours as your clock time, you cannot use AM or PM. That is only when you use 12 hours' time to indicate if it is AM or PM.
Now, to your question: 20:40 hours is the same as 20:40 - 12=8:40PM +1:40=9h + 80m. But, an hour is 60 minutes, so we have:80 - 60=20 minutes. Or 9h + 1h + 20m=10:20PM. Or, 10:20 + 12=22:20h.
