The thirty Nine Steps (1978) - the third of at least four film versions of the 1915 John Buchan thriller.
Richard Hannay attempts to stop the minute hand of Big Ben reaching 45, thus setting off a bomb.
Robert Powell as Richard Hannay, in a cliffhanger near the end that wasn't in the original book.
11:41am to 11:44am.
Three minutes of film in real time.