at

• Use at for specific times, holidays without the word "day," and other fixed points in time.
• Examples:
• at 7:00 a.m.* — We have class at 7:00 a.m.
• at noon* — Lunch is at noon.
• at midnight* — The show starts at midnight.
• at Christmas* — We visit family at Christmas.

on

• Use on for specific days and dates.
• Examples:
• on Monday* — The meeting is on Monday.
• on October 5th* — Her birthday is on October 5th.
• on Friday night* — We’re going out on Friday night.
• on New Year’s Day* — The parade is on New Year’s Day.

in

• Use in for longer periods (months, years, centuries), parts of the day, and general time frames.
• Examples:
• in July* — We’re traveling in July.
• in 2023* — This book was published in 2023.
• in the morning* — I exercise in the morning.
• in the 21st century* — Many changes happened in the 21st century.

Tips

• Use at for precise times (at 3 p.m., at sunrise).
• Use on for days and dates (on Tuesday, on July 4th).
• Use in for longer or less specific times (in the afternoon, in June, in two hours).
• Some expressions are fixed and don’t change (at night, at dawn).

Summary

• at = exact times or specific points (at 9:00, at Christmas)
• on = specific days/dates (on Monday, on April 1st)
• in = longer periods or parts of the day (in May, in the evening)