Std post field ‘post_modified’ hour display format ?

Below is a shortcode [datetime] which will output the current post object’s modification date according the the date and time format set on /wp-admin/options-general.php.

The default setting includes am/pm. See https://www.php.net/manual/en/datetime.format.php for guidelines on how to set alternative formats on that settings page, such as 24-hour time.

See the comments below for links to additional documentation & how to output the published date instead of the modified date.

The shortcode outputs the timestamp in a <p> tag. If it is to be used within content already in a paragraph or other tag, remove <p> and </p>, or remove return sprintf( and instead start the function at return wp_date(, removing one of the ending-closing-parenthesis.

<?php

/**
 * [datetime]
 * 
 * @see /wp-admin/options-general.php (For date & time format settings.)
 * @see https://developer.ww.wp.xz.cn/reference/functions/wp_date/
 * @see https://developer.ww.wp.xz.cn/reference/functions/get_post_timestamp/
 * @see https://www.php.net/manual/en/datetime.format.php
 * @see https://www.php.net/manual/en/function.sprintf.php
 */
add_shortcode(
	'datetime',
	function( $atts, $content, $tagname ) {
		return sprintf(
			'<p>%s</p>',
			wp_date(
				sprintf(
					'%s %s',
					get_option( 'date_format' ),
					get_option( 'time_format' )
				),
				get_post_timestamp(
					get_the_ID(),
					'modified' // change to 'date' for published date.
				)
			)
		);
	}
);