# MDY 24-Hour Datetime Key: `datetime.timestamp.mdy_24h` Month/Day/Year date ordering (MM/DD/YYYY) with 24-hour time. Common in US military, healthcare, and technical systems. Page: Format: `%m/%d/%Y %H:%M:%S` Samples: `01/15/2024 10:30:00`, `12/31/2019 23:59:59` ## Background ### Origin FineType defines this type as month/day/year date ordering (MM/DD/YYYY) with 24-hour time.[[1]](https://github.com/meridian-online/finetype/blob/main/labels/definitions_datetime.yaml) FineType's label definition gives the type the format string %m/%d/%Y %H:%M:%S.[[1]](https://github.com/meridian-online/finetype/blob/main/labels/definitions_datetime.yaml) In the United States, dates are traditionally written in month-day-year order.[[2]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) The slash is the most commonly used separator in the all-numeric form of the American month-day-year date.[[2]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) The 24-hour clock is used in military, public safety and scientific contexts in the United States.[[2]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) In the United States, 24-hour notation is also widely used by astronomers, hospitals and public safety personnel.[[2]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) Wikipedia's article on American date and time notation explains hospital use of the 24-hour clock by the danger of mistaking 5:00 AM for 5:00 PM when medication is due.[[2]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) The type is best read as a meeting of two American habits: the civilian month-first date and the unambiguous 24-hour time of settings where AM and PM must not be confused. (Meridian's view) ### Use According to Wikipedia, the Chicago Manual of Style discourages all-numeric dates other than the ISO 8601 year-month-day form, because they are not comprehensible to readers outside the United States.[[2]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) In a file that travels, the order is the weak point: a value such as 03/04/2024 10:00:00 reads sensibly as month-first or day-first, and nothing in the string says which was meant. (Meridian's view) Before trusting a column, look for a value whose first field is above 12, or whose second field is, to settle which order the file uses. (Meridian's view) In Python's strftime() and strptime() format codes, %m is the month as a zero-padded decimal number.[[3]](https://docs.python.org/3/library/datetime.html) In Python's format codes, %H is the hour on the 24-hour clock as a zero-padded decimal number.[[3]](https://docs.python.org/3/library/datetime.html) Python's documentation says that when strptime() is used, the leading zero is optional for formats including %d, %m, %H, %M and %S.[[3]](https://docs.python.org/3/library/datetime.html) Python's datetime.strptime() raises ValueError if the date string and format cannot be parsed by time.strptime().[[3]](https://docs.python.org/3/library/datetime.html) DuckDB's strptime function throws an error on failure.[[4]](https://duckdb.org/docs/current/sql/functions/dateformat.html) DuckDB's try\_strptime function returns NULL on failure.[[4]](https://duckdb.org/docs/current/sql/functions/dateformat.html) DuckDB lets a date or timestamp format be specified during CSV parsing, in a COPY statement or in the read\_csv function.[[4]](https://duckdb.org/docs/current/sql/functions/dateformat.html) Parse with the explicit format string rather than a guessing parser, and prefer the variant that returns NULL so that rows which fail can be counted rather than silently lost. (Meridian's view) Unless the source documents a time zone, treat the values as local wall-clock time. (Meridian's view) ### Where you'll meet it Klaviyo's developer documentation lists 09/15/2021 13:34:08 among the supported formats for dates and timestamps in profile and event properties.[[5]](https://developers.klaviyo.com/en/v1-2/docs/acceptable-date-and-timestamp-formats-for-profile-and-event-properties) Klaviyo's documentation says dates must be formatted as either YYYY-MM-DD or MM/DD/YYYY.[[5]](https://developers.klaviyo.com/en/v1-2/docs/acceptable-date-and-timestamp-formats-for-profile-and-event-properties) Klaviyo's documentation says dates cannot be formatted in the DD-MM-YYYY format.[[5]](https://developers.klaviyo.com/en/v1-2/docs/acceptable-date-and-timestamp-formats-for-profile-and-event-properties) ## Sources 1. [finetype/labels/definitions\_datetime.yaml at main · meridian-online/finetype · GitHub](https://github.com/meridian-online/finetype/blob/main/labels/definitions_datetime.yaml) — FineType 2. [Date and time notation in the United States - Wikipedia](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) — secondary source 3. [datetime — Basic date and time types — Python 3.15.0 documentation](https://docs.python.org/3/library/datetime.html) — documentation 4. [Date Format Functions – DuckDB](https://duckdb.org/docs/current/sql/functions/dateformat.html) — documentation 5. [Acceptable date and timestamp formats for profile and event properties](https://developers.klaviyo.com/en/v1-2/docs/acceptable-date-and-timestamp-formats-for-profile-and-event-properties) — organisation