date-modified.php

<?php
/**
 * Displays the post modified date.
 *
 * @package  There is no package.
 */

/**
 * Returns the last modified date for the post with the <time> tag and the
 * time zone.
 *
 * @parameter array $arr Allowed tags.
 * @parameter string $tz The post modified time.
 * @parameter string $ltz The local timezone offset.
 * @parameter string $modified_time The unsanitized output.
 * @parameter string $output The sanitized output.
 *
 * @return string The sanitized output.
 */
function my_post_modified_date() {
	$arr = array(
		'time'  => array(
			'datetime' => array(),
		),
		'small' => array(),
		'i'     => array(),
	);

	$tz = get_the_modified_time( 'T' );
	if ( 'CST' === $tz ) { // Standard Time. Change to match your timezone.
		$ltz = '-6:00'; // Change the offset to match your timezone.
	} elseif ( 'CDT' === $tz ) { // Daylight Saving Time. Change to match your timezone.
		$ltz = '-5:00'; // Change the offset to match your timezone.
	} else {
		$ltz = '';
	}

	$modified_time = '<small><i>' . esc_html_e( 'Latest revision:', 'text-domain' ) . '</i> <time datetime="' . get_the_modified_time( 'Y-m-d\TG:i:s', true, null, true ) . $ltz . '">' . get_the_modified_date() . '</time></small>';

	$output = wp_kses( $modified_time, $arr );
	return $output;
	// Use a standard WordPress hook to output the string to your post.
	// See https://developer.wordpress.org/plugins/hooks/.
}