The dashed frame shows a clock as it appears in a mirror. What will the mirror image show 1 hour 40 minutes later?

The image shows 1:20, so the real time is 11:60 - 1:20 = 10:40. 1 hour 40 minutes later it is 12:20, whose mirror image is 23:60 - 12:20 = 11:40. The image runs backwards: 1:20 - 1:40 = 11:40. (3:00 adds the time to the image; 12:20 is the new real time.)