Add Last Modified Column to Posts

<?php
if ( ! function_exists( 'scseed_add_modified_column' ) ) {
    function scseed_add_modified_column( $columns ) {
        $columns['scseed_modified'] = __( 'Last Modified', 'scseed' );
        return $columns;
    }
}
if ( ! function_exists( 'scseed_show_modified_column' ) ) {
    function scseed_show_modified_column( $column, $post_id ) {
        if ( 'scseed_modified' !== $column ) {
            return;
        }
        echo esc_html( get_post_modified_time( get_option( 'date_format' ) . ' ' . get_option( 'time_format' ), false, $post_id ) );
    }
}
if ( ! function_exists( 'scseed_sortable_modified_column' ) ) {
    function scseed_sortable_modified_column( $columns ) {
        $columns['scseed_modified'] = 'modified';
        return $columns;
    }
}
add_filter( 'manage_posts_columns', 'scseed_add_modified_column' );
add_action( 'manage_posts_custom_column', 'scseed_show_modified_column', 10, 2 );
add_filter( 'manage_posts_sortable_columns', 'scseed_sortable_modified_column' );