The most common PREPOSITIONS OF TIME are "at, in, on".
We use:
- "at" for a Precise Time, e.g. at noon / at 3 PM / at 1:45 (one forty-five)
- "in" for Months, Years, Centuries and Long Periods, e.g. in April / in 2015 / in the 21st century / in three hundred years
- "on" for Days and Dates, e.g. on Wednesday / on April 22