Both the 12-hour clock and the 24-hour clock are used in the United States, although the 12-hour clock is more common. The use of the 24-hour clock is usually restricted to transportation (bus, train, and airline) schedules and the military.
When we use the 12-hour clock, it is conventional to label:
The English term "morning" implies all times to which we might apply the AM label. It is common to use qualified forms such as "early morning", "mid-morning", and "late morning", although there is no widely accepted convention as to precisely which parts of the morning these terms apply, and to obtain clarity one should ask for a specific time. The English term "afternoon" is applied to times following noon, but preceding times to which the term "night" might be applied; however, once again, since there can be great variation in the time of onset of darkness in the temperate zones, these terms are imprecise, and, again, to obtain clarity one should ask for a specific time. There is, however, a conventional context in which the terms "afternoon" and "evening" are employed differently than the term "night": when meeting someone after noontime, it is conventional to wish them "Good afternoon" or "Good evening", where the latter greeting is more appropriate later in the day; however, the phrase "Good night" is conventionally used only when taking leave of them.
There are many common usages in speaking the time. Times "on the hour" such as 7:00AM may be said as
Times "at the quarter hour", such as "7:15AM" may be said as
Times "at the half hour", such as "7:30AM" may be said as
Times "at the three-quarter hour", such as "7:45AM" may be said as
Times other than the above four classes may also be said in several ways; for instance, "7:55AM" may be said as
Times within the first ten minutes past the hour have one more common usage: for instance, consider 9:09AM: the zero is often pronounced as "oh" (because of the resemblance of the digit 0 to the letter O); thus we might say "nine oh nine AM" or "nine oh nine in the morning" in addition to "nine nine AM", etc., as described previously.
The seven days of the week in English are "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", and "Saturday". Sunday and Monday are named for the Sun and the Moon, which were the most important of the pre-Copernican planets; Saturday is named for the planet and the Roman god "Saturn"; the remainder are named for gods of Germanic mythology ("Tiw", "Woden", "Thor", and "Frige").
In the United States, the week is usually considered to begin with Sunday and, therefore, to end with Saturday, and this is how weeks are displayed in calendars. Saturday and Sunday, taken together, constitute the "weekend"; the remaining days are called "weekdays" or "workdays", the latter term recognizing that many Americans neither work nor attend school on weekends.
The twelve months of the calendar year in English are, in order, "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", and "December". The names of the months are Roman in origin. It is common to abbreviate month names with their first three letters.
The seasons in English are, in order of their occurrence in the calendar year, "winter", "spring", "summer", "autumn" or "fall", and, again, winter. The seasons are generally taken to start at specific astronomical events; thus
The precise date (and often time) of these events are usually announced on mass media.
It is American tradition to open public swimming pools on Memorial Day weekend—the last weekend in May—and to close them on Labor Day weekend—the first weekend in September. The long Summer vacation for schools in New York usually begins in late June, and ends shortly after Labor Day (the first Monday in September). Labor day thus marks the end of Summer for many.