There are three prepositions in English that are used with Time: '
in', '
at' and '
on'.
Generally, 'in' shows the “largest” time or place,
'on' shows dates and time,
and 'at' usually shows the “smallest” time or place:
Examples:
The Winter Olympics were held in Vancouver in 2010.
We usually go out on Saturday evenings.
Brad usually eats his lunch at 12:00.