Prepositions of time show when something happens, how long it lasts, or where it sits in a time line. In English, they come before a noun phrase, such as at five, in July, or for two hours. If you remove the preposition, the time expression often becomes unclear or ungrammatical. A sentence like She left Friday sounds incomplete in standard English, while She left on Friday gives the time clearly. These forms are part of the larger system of Prepositions, and they often work inside the Prepositional Phrases you use to add time information to a sentence.

Exact moments and clock times

Example	Pattern
The train leaves at six o'clock.	Use at for a specific clock time or exact moment.
We visit my grandparents at Christmas.	Use at for short holiday expressions.
Please call me at noon.	Use at for a point in the day when you mean a precise time idea.

Use at with exact times on a clock: at 8:00, at 3:30, at midnight, at noon. It also appears with short time expressions that point to a precise moment, such as at sunrise or at bedtime. Place at directly before the time expression. Say The train leaves at 6:15, not The train leaves 6:15. The same pattern works when you talk about an appointment, a meeting, or a specific point in the day: We met at lunch, She called at the last minute. For place and movement around locations, compare this with Prepositions of Place and Prepositions of Direction, where the preposition gives a different kind of information.

Longer time periods and parts

Example	Pattern
I moved here in April.	Use in with months, years, and seasons.
She studies in the morning.	Use in with parts of the day.
We will finish in two weeks.	Use in for longer periods of time.

Use in with longer time periods: in April, in 2026, in summer, in the morning, in the afternoon. These expressions do not point to one exact moment. They place an event inside a month, year, season, or broad part of the day. Put in before the time phrase, as in We travel in August and The museum closes in the evening. With parts of the day, in is normal for in the morning, in the afternoon, and in the evening. For periods of time in general, in can also show how long something takes: in two weeks means before two weeks pass.

Specific days and calendar dates

Example	Pattern
The class is on Tuesday.	Use on with days of the week.
My birthday is on July 10.	Use on with exact dates.
We met on Friday morning.	Use on with a day name plus a date.

Use on with days, dates, and specific day names: on Monday, on July 4th, on my birthday, on New Year’s Day. It marks a day as a particular point in time, more specific than in but less exact than at. Place on before the day or date: The class is on Tuesday, They arrived on 15 May. When the day expression is long, on still stays in front: on the first Monday of the month. In everyday English, this pattern also appears with holidays and named days, such as on Christmas Day.

Length and time reference patterns

Usage	Explanation	Example
Activity period	Use during when something happens inside a period or event.	I felt sleepy during the meeting.
Duration	Use for to say how long something lasts.	We waited for an hour.
Starting point	Use since with a point in time that began earlier and continues now.	She has lived here since 2020.

Use during when something happens inside a period or event: during the meeting, during the winter, during the film. It tells you that another action takes place within that time span. Use for to show a length of time: for three hours, for a week, for years. It answers the question of how long. Use since with a starting point that continues up to now: since Monday, since 2022, since breakfast. With since, the action began at that point and is still connected to the present. In a sentence, She has worked here since May and She has worked here for five months give different information: one gives the starting point, the other gives the duration.

Deadlines and time ranges

Usage	Explanation	Example
Deadline before a time	Use by to mean something happens no later than a time.	Please finish it by Friday.
Starting point of a range	Use from to show when a period begins.	The office is open from nine.
Ending point of a range	Use until to show a period continues up to a time.	Stay here until five.
Full time span	Use to after from to show the end of a time range.	The shop is open from Monday to Friday.

Use by for a deadline or a latest time: by Friday, by 6:00, by the end of the month. The action must happen at or before that point. Use from...to to show the beginning and ending points of a time range: from 9:00 to 5:00, from Monday to Wednesday. Use until to show that something continues up to a point in time: We stayed until midnight. The form to can also appear in a range, usually after from, as in from January to March. The difference is in the idea: by points to a limit, while from...to and until describe the span itself.

Some time expressions are fixed phrases, so they do not follow the usual choice of preposition one word at a time. Say at night, in the morning, in the afternoon, in the evening, on time, and in time. These phrases are learned as complete chunks and are used that way in daily English. At night refers to the period of darkness as a general time, not one exact clock moment. On time means at the planned or expected time. In time means early enough for something to happen. These patterns also appear in regular conversation about work, travel, and appointments, and they fit naturally with the time expressions taught in Common Prepositions.

Regional and fixed time contrasts

Region	Variant	Definition	Example
United Kingdom	at the weekend	Use at the weekend in British English to talk about the weekend in general.	We go hiking at the weekend.
United States	on the weekend	Use on the weekend in American English to talk about the weekend in general.	We go hiking on the weekend.
International	in time	Use in time to mean early enough for something to happen.	I arrived in time for the movie.
International	on time	Use on time to mean punctually at the expected time.	The meeting started on time.
International	at the end	Use at the end to point to the final moment of a period or event.	We were tired at the end of the trip.
International	in the end	Use in the end to mean finally after a process or decision.	In the end, we chose the blue jacket.

Scramble

English has a few time expressions that vary by region or meaning. In British English, people usually say at the weekend; in American English, on the weekend is common. Both mean the same period of Saturday and Sunday. The expressions in time and on time are not the same: on time means punctually, while in time means with enough time before a result or event. The pair at the end of and in the end also differ: at the end of points to the final part of a period, while in the end means finally or after a process. These fixed uses belong to the wider system of Prepositions and are needed for accurate time phrases in everyday English.