Prepositions – time
I have my holiday in July.
I bought this house in 2014.
I can do it in ten minutes.
She comes at 9 every day.
I don’t have it at the moment.
He called me at noon.
I play tennis on Monday.
She visited me on my birthday.
I work only for six hours every day.
I have been running for 20 minutes.
When we speak about some longer period of time, we use in.
When we can do something during some time, we also use in.
When we speak about one moment in time, we use at.
When we speak about a day, we use on.
When we do something for some time, we use for.
Sometimes you can find exceptions to these rules. For example, at night.
On the fifth day, I learnt another secret of the little prince’s life.
The flowers appeared in the grass in the morning.
If you could fly to France in one minute, you could watch the sunset.
At sunrise, the flower showed herself.
The little prince looked at the snake for a long time.
You can see more examples in the book The Little Prince.