Days of Future Past: Part 2 - S1-E12
Continuity mistake: When Xavier's watch magnetically clings to his hoverchair, the body of the watch is pointing at 1 o'clock. In the next shot, it is pointing at 12 o'clock, the minute hand has advanced roughly 4 minutes, and the watch has also moved down the chair and to the right a few inches (note the contour lines on the chair as the visual cue). (00:20:39)