Preposition of time

On

Days of the week

He has a meeting on Monday.

They play tennis on Saturday.

special days

I will visit my grandparents on Christmas Day.

They go out on New Year's Eve.

Specific dates

Her birthday is on July 15th.

We have an event on October 31st.

In

long periods of time

Cars became popular in the 20th century

Fashion trends changed a lot in the 1990s.

Parts of the day:

I drink coffee in the morning.

He goes for a run in the morning.

Future or Past Time Periods:

In the past, people used to write letters.

In the future, we might live on other planets.

At

Specific hours

The movie starts at 7 p.m

He wakes up at 6 a.m

Specific moments

She feels relaxed at night.

They go to bed at midnight.