Clocks “fall back” in autumn, or fall.

“To fall back … suggests that one must set the clocks one hour back when Daylight Saving Time ends. It is associated with the fall (autumn) season because the DST schedule ends in the fall. The fall season and the end of daylight saving time mark a period when the days start getting shorter, with fewer hours of sunlight.

“Records have shown that the phrase spring forward, fall back has been in use at least as far back as early 20th century. For example, the Heppner Gazette-Times (October 28, 1928) printed a notice, stating “Daylight Savings Time ends this Sunday, October 31. Remember to set your clocks back one hour, ‘Spring forward – Fall Back!’”.

Read more about time at timeanddate.com