: What format should I use when beginning a chapter with the time and location of the events? What format should I use when beginning a chapter with the time and location of the events? I was

The short answer is, you can do this any way you want. But how you do it will set the tone for the story.

If you write it in a log format, it will bring to mind military experiences or a formal log for a job (like a medical record).

For example, here is a World War II era U.S. Naval log. The starting location is given for each day and each entry has the time in 24 hour format minus the standard colon. The date is given with the day then the day-month-year which is military and international.
(I'm including headers from the page that you wouldn't necessarily put in a book...though if you did, it would be just the first time, if it was from the same log.)

U.S.S. CRUX (AK-115) c/o Fleet Post Office San Francisco, Cal.

CONFIDENTIAL

Wednesday, 19 April 1944

Moored to berth #1A , Norfolk Navy Yard, Portsmouth, Virginia.

1015 — Loaded two thousand (2000) rounds 20mm ammunition.
1430 — Loaded six hundred (600) rounds 40mm ammunition.

A medical record uses the time if there are multiple entries per day (such as in a hospitalization) and it's usually in military format. The date can be abbreviated or written out. The location is in the header.

June 3, 2019, 1320 hours

OR

06/03/2019

A diary or letter format will bring to mind a single character setting her/his thoughts to paper. In the US, the standard is month-day-year. The day of the week and the time are optional and up to the writer. A location is generally only there if it's different from the usual places the author writes, like if s/he is on vacation.

June 3, 2019. Monday, 1:20pm.

OR

Monday, Jun 3, 2019. Camping at the American River

For a standard "here's where the characters are right now!" format, just give the facts in a non-military format. Use 12 hour time if you're American (Europeans use 24 hour time even if not in the military). I would write out the date so it's easy to read, and use the American format (again, unless you're not in America). I would not put "in" and other elements to create sentence structure. This is factual information, not a narrative. And don't spell out numbers. Don't say "USA" if you're giving a state, unless the readers aren't in the US and don't know the book is set there (or if only one scene is set there). There's also no need to put the state if it's a famous city like LA.

Sunday, June 2, 2019. 9pm. Los Angeles.

OR

Jun 2, 2019, Sunday night, Los Angeles.

OR

Los Angeles, 9 PM. Sunday, June 2, 2019.

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If you're doing a time stamp (i.e. no one is narrating the time, but each chapter is chronologically ordered but not in a linear way (i.e. flashbacks, or chapter 1 and chapter 2 starting at the same moment in time) or you are depicting actions happening in different parts of the world and time zones are involved, Military time is usually used to distinguish morning and afternoon times (Midnight is 0000 and each hour is +0100). In dialog, leading zeroes are stated so 0100 is "Zero-One-Hundred Hours" (There may be some people who say "Oh" instead of "Zero). 2 digit hours (1000-2300) are prononced "Ten-Hundred Hours". If the time includes minutes, all numbers numbers are pronounced in or as individual digits. 0543 is "Zero-Five-Four-Three". Although rarely seen in fiction, time zones have a single letter designation and are pronounce using the NATO Alphabet. The most likely to be seen is "Z" (Zulu) which is Greenwich Mean Time. Less likely "J" Juliette is the local time zone.

Typically these aren't favored as they don't give a good heads up to civvilain readers. Typically fiction will use either the three letter value (so the time in L.A. Would be noted to be time in P.S.T. or Pacific Standard Time. Or peg time to the a large city in the time Zone (E.S.T is also called New York City Time. Greenwich Mean Time is also London Time.

I highly suggest a format similar to that on "Young Justice" which actually time stamps all their scenes (One of the writers always has dates for events depicted in an episode in his previous works, but YJ put them up for the fans who knew this.). The best display of this is the opening scene of the very first season, which depicts four of the main characters and their respective mentors battling ice themed villains. If you pay attention to the sequence, It's all at the same time across multiple time zones (Specifically, EST, CST (Central Time), PST, and HST (Hawaii/Honolulu time).

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It kind of depends, to my way of thinking at least, on who the narrator of the tale is; if they are a disembodied third person POV then it's more or less authors choice, pick something you like and stick with it consistently. If, on the other hand, you're using a character from the narrative as the storyteller then you have to decide how your character thinks about time and use a consistent format in keeping with their background. For example if Steve has worked anywhere that deals with 24/7 scheduling he's likely to use 2100 rather than 9pm.

As a note if you're going to head one chapter head them all, otherwise get your characters to keep track of time "in narrative" instead:

Steve got out of the office earlier than usual, and took a cab to meet his friend who was sitting on a park bench by his lonesome.
"Come on it's only 9, the night is young." he said by way of greeting and they...

This can be more organic and if you don't need to keep constant track of time throughout the whole narrative then it requires less attention from the reader than a separate header. You can do it as you need it, when you need it, to keep events in order when it matters and not worry about it when the narrative timeline is linear.

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Depends. If it's a one-off indication, you should introduce it as prose: "It was 9 P.M. on a Sunday in Los Angeles..."

But I assume that's not the case, maybe you're writing a thriller, and you're going to point out the changes in location explicitly multiple times during narration, like X-Files does.

If that's the case, then I would introduce the change of location using italics or a monospaced font, maybe after a scene break introduced by an asterism (three horizontally-centered asterisks).

Los Angeles, CA, USA
Sunday
9 P.M.

Steve got out of the office earlier than usual, and took a cab to meet his friend who was sitting on a park bench by his lonesome.

An alternative is using right-aligned text and small caps, like this page from the Sorrows of Werther, a novel written as a diary.

In any case, if you're going to do this multiple times, no matter the stylistic choice you go with, clearly separate the location and time from the rest of narration.

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