Hi Rick,
Sorry for not getting back to you sooner!
You should be able to do this:
add_filter( 'wpsp_date_output', 'tu_wpsp_relative_date' );
function tu_wpsp_relative_date() {
echo '<span class="wp-show-posts-posted-on wp-show-posts-meta">' . human_time_diff( get_the_time( 'U' ), current_time( 'timestamp' ) ) . ' ago</span>';
}Let me know 🙂