After learning about prepositions of place, let us now review the correct usage of prepositions of time. The most commonly used prepositions of time are surprisingly the same as propositions of place: at, on, and in. They are used as follows.
1.) At is usually used at precise time: at 7:00 o’clock, at midnight, at bed time, at Christmas, at the end of the week.
2.) In is used for longer periods of time such as months, years, seasons, part of the day and duration. For example, in May, in 2015, in summer, in the evening.
3.) On is used with days and dates. For example, on Monday, on June 21.
Notice that on is usually more precise than in such as “in Friday” and “on Friday evening.” » Read more