AM was a period of the day opposite to PM, (TV: The Sontaran Stratagem) being the period of time in the first half of a given day. British Summertime began in early 2005 on a Sunday morning at 01:00am when the clocks went forwards. (PROSE: The Clocks Go Forward)
On 13 February, 13,500,017,093 BC, the beginning of the universe occurred at 11 am. (PROSE: Time Traveller's Diary)