WordPress at a glance
function is not described

get_post_modified_time() WP 2.0.0

Retrieve the time at which the post was last modified.

Hooks in function
Return

String/Int/false. Formatted date string or Unix timestamp if $id is 'U' or 'G'. False on failure.

Usage

get_post_modified_time( $d, $gmt, $post, $translate );
$d(string)
Format to use for retrieving the time the post was modified. Either 'G', 'U', or php date format.
Default: 'U'
$gmt(true/false)
Whether to retrieve the GMT time.
Default: false
$post(int/WP_Post)
WP_Post object or ID.
Default: global $post object
$translate(true/false)
Whether to translate the time string.
Default: false

Code of get post modified time: wp-includes/general-template.php VER 5.0.3

<?php
function get_post_modified_time( $d = 'U', $gmt = false, $post = null, $translate = false ) {
	$post = get_post($post);

	if ( ! $post ) {
		return false;
	}

	if ( $gmt )
		$time = $post->post_modified_gmt;
	else
		$time = $post->post_modified;
	$time = mysql2date($d, $time, $translate);

	/**
	 * Filters the localized time a post was last modified.
	 *
	 * @since 2.8.0
	 *
	 * @param string $time The formatted time.
	 * @param string $d    The date format. Accepts 'G', 'U', or php date format. Default 'U'.
	 * @param bool   $gmt  Whether to return the GMT time. Default false.
	 */
	return apply_filters( 'get_post_modified_time', $time, $d, $gmt );
}