the_title
filter filters the existing title when it’s output on the front end. If you want to set a title when a post is created on the back end, you want to use the title_save_pre
filter:
function wpa65253_time_title( $title ) {
global $post;
if ( isset( $post->ID ) ) :
if ( empty( $_POST['post_title'] ) && 'time' == get_post_type( $post->ID ) )
$title="sample headline";
endif;
return $title;
}
add_filter ( 'title_save_pre', 'wpa65253_time_title' );