According to [the Codex page for `get_the_time()`](http://codex.wordpress.org/Function_Reference/get_the_time), it needs to be used in The Loop.  The difference between [`the_time()`][1] and [`get_the_time()`][2] is that the former [`echo()`][3]es the date, and the latter returns it.

There are a couple functions that do what I think you're looking for -- get the last updated date and time for a post:  [`get_the_modified_time()`](http://codex.wordpress.org/Function_Reference/get_the_modified_date) and [`get_the_modified_date()`](http://codex.wordpress.org/Function_Reference/get_the_modified_date).  It looks like they too need to be used in [The Loop][4].

Here's one way to get the updated date of the most recent post in your site:

    <?php
         $args = array(
            'orderby'     => 'post_modified',
            'numberposts' => 1,
        );
        $myposts = get_posts( $args );
        if( have_posts() ) {
            while( have_posts() ) {
                the_post();
                $last_update = get_the_modified_date();
            }
        }
        echo( "Last modified on $last_update." );
    ?>

If you're sure you need to be outside of any Loops, you can always use [`$wpdb`](http://codex.wordpress.org/Function_Reference/wpdb_Class):

    <?php
        global $wpdb;
        $sql = "SELECT post_modified
                FROM $wpdb->posts
                WHERE post_type='post'
                AND post_status='publish'
                ORDER BY post_modified DESC
                LIMIT 1";
        $last_update = $wpdb->get_var( $sql );
        echo( "Last updated $last_update." );
    ?>


  [1]: http://codex.wordpress.org/Function_Reference/the_time
  [2]: http://codex.wordpress.org/Function_Reference/get_the_time
  [3]: http://php.net/manual/en/function.echo.php
  [4]: http://codex.wordpress.org/The_Loop