In, on or at for time: days, dates and clock times

Put at before a time shown on a clock, such as 8:15 or six o'clock. Noon means twelve in the middle of the day, and midnight means twelve at night; these also take at.

At tells the listener when an event happens. The whole phrase can come after the action or at the start of the sentence. The preposition does not change because you move the phrase or change the subject.

Use on with the name of a day or a full calendar date. A date names a particular day within a month. Adding a year to the date does not change on to in, because the phrase still names a day.

A plural day such as Mondays can describe something that happens every Monday. On my birthday and on the first day also name days, even though they are not weekday names.

Use in before a month, a year or a season. These phrases place an event within a period without naming an exact day. A month followed by a year still uses in.

You can often say in summer or in the summer, and the same choice is possible with the other seasons. This grammar does not tell you what the weather is like. Choose a season that fits the place and event you are describing.

Use in the morning, in the afternoon and in the evening when no particular day is named. Keep the before morning, afternoon and evening in these phrases.

At night is the usual phrase for night in general. In the night is also possible when you mean during a particular night, for example when something wakes you. Do not treat every use of in the night as a mistake.

A named day changes the phrase: in the morning becomes on Monday morning. The same pattern works with afternoons and evenings. Read the whole time phrase before you choose a preposition.

On also introduces a morning or evening identified in another way, such as the morning of a particular date. The word morning alone does not decide the preposition. Compare a general part of the day with one tied to a particular day.

Ordinary time expressions beginning with this, next, last, every or each usually need no in, on or at. Use the whole phrase directly after the action or at the beginning of the sentence.

Today, tomorrow, yesterday and tonight also work without these prepositions. A nearby clock time can still have at. This means one sentence can contain a time phrase with no preposition and another phrase with a preposition.

In American English, on the weekend and on weekends are common. In British English, you will often hear at the weekend and at weekends. Both patterns are standard; in the weekend is not the usual choice in either variety.

A celebration can mean a whole holiday period or a particular day. British English commonly uses at Christmas for the period and on Christmas Day for the day. If a phrase names a specific day, on is the useful pattern, including on New Year's Day.

With a future event, in followed by an amount of time can tell us how far away that event is. In ten minutes means ten minutes from now in this use. It is different from a clock time such as at ten.

To say how long an activity continues, use for with the amount of time. In has another use for the time needed to finish a task, as in making something in ten minutes. The verb and situation help you decide whether in points to a future start or a completed task's time.

When a sentence gives more than one time detail, choose the preposition for each phrase. A day can take on while a clock time in the same sentence takes at. A month can take in even if another part of the sentence mentions a day.

Several orders are natural. You can put the day before or after the clock time, provided the sentence is clear. When checking your writing, look for the whole time phrase, including words such as next or every, before adding a preposition.