 According to Back to the Future Part III (1990), 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 that Doc Brown  gives Marty at the end of Back to the Future Part III (1990). The  time is provided by the mayor in Back to the Future Part III (1990),  who starts it. 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, 24 days, 2 hours, and 4 minutes.