WordPress at a glance
filter is not described

get_lastpostdate filter-hook . WP 2.3.0

Filters the date the last post was published.

Usage

add_filter( 'get_lastpostdate', 'filter_function_name_8009', 10, 2 );
function filter_function_name_8009( $date, $timezone ){
	// filter...

	return $date;
}
$date(string)
Date the last post was published.
$timezone(string)
Location to use for getting the post published date. See get_lastpostdate() for accepted $timezone values.

Where the hook is called

get_lastpostdate()
wp-includes/post.php 5878
return apply_filters( 'get_lastpostdate', _get_last_post_time( $timezone, 'date', $post_type ), $timezone );

Where the hook is used (in WP core)

Does not used.