The clock in the clock tower started running at 8:00 p.m. on September 5, 1885. The date is provided by the caption on the photograph Doc gives Marty at the end of the movie. The lightning strikes the clock tower at 10:04 p.m. on November 12, 1955. This means that the clock tower operated for exactly 70 years, 2 months, 7 days, 2 hours, and 4 minutes.
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