What time will it be 8 hours from now? Add eight hours to the time on your clock and leave the minutes exactly as they are. At 7:10 AM, the answer is 3:10 PM the same day.
What time will it be 12 hours from now? Add twelve hours to the time on your clock and the minutes never move. At 9:44 AM, the answer is 9:44 PM the same day.
What time was it 11 hours ago? Move the hour on your clock back by eleven and leave the minutes untouched. At 6:15 PM, that gives 7:15 AM the same morning. The tricky part is the date, because eleven hours is long enough to reach back across midnight for almost half of the day.
What time was it 5 hours ago? Take the time on your clock and move the hour back by five. If your clock says 1:00 PM, five hours ago it was 8:00 AM. The minutes and seconds stay exactly as they are.
Need to know what time was it 6 hours ago? Look at your clock and count back six hours. At 3:00 PM, the answer is 9:00 AM. The minutes and seconds never change. Only the hour moves, and sometimes the date does too.