IN is used when talking about months, years, and long time periods such as centuries, seasons or the future.
- In 2009, a strong typhoon attacked the Philippines and left many damages.
- I might visit your country in August.
- We will start the new project in January 2014.
- I haven’t seen you in centuries!
- I hope we see each other in the future.
- In spring, many flowers bloom.
ON is used for dates and days.
- The organization will be having its 20th Anniversary on July 7, 2010.
- On June 6, she will start to work.
- Our family gathers together on New Year’s Eve.
- My friends surprised me on my birthday.
- She has no class on Mondays.
AT is used for specific or precise time.
- We will start our class at 9 o’clock.
- We usually eat together at dinnertime.
- She was very upset at that moment.
- At noon time, the participants will have their lunch break.
- The sun was very beautiful at sunset.
Is it clear now? I hope this post helps.
Of course, you will be able to learn these words easily if practice them. Good luck! \(^-^)/