Prepositions of time - AT, IN, ON

Sometimes it's hard for students to understand and distinguish these three prepositions of time. Here is something to help you:

in - longest times (eg.: In 1976)

on - dates (On  February 2nd)

at - shortest times (at 4 o'clock, at Christmas)

In “longest  time”	On “dates/special dates”	At “shortest time”
In 2011 In October In the 18th century In the Summer In the evening In the morning In the Easter holiday	On Monday On 3rd December On this day On Christmas Day On Easter Sunday On Wednesday morning	At two o’clock At the moment At dinner At Christmas At the weekend At night

Try these exercises:
http://www.ihbristol.com/learn-online/exercise-general/elementary/grammar/prepositions-of-time/98/
http://www.englishforjapanese.com/exercises/prepositions/02%20preps.html