A. Principles
We use:
AT for the time of day:
- at six o’clock at 11.15 at midnight
- at lunchtime at noon at sunset etc…
ON for days a and
dates
- on Monday/ on Mondays on 16 October 1989 on my birthday
IN for longer periods (months/ years/ seasons)
- in October in 1989 in the 21st century in the past
- in (the) winter in the 1960s in the Middle Ages in (the) future