Restrict Jetpack's Related Posts to a specific time-frame

jp_restrict_rp.php

function jetpackme_related_posts_date_restricted( $date_range, $post_id ) {
    // We can change this based on $post_id too but let's just filter everything
    $date_range = array(
        'from' => strtotime( '1 January 2013' ),
        'to' => time(),
    );
    return $date_range;
}
add_filter( 'jetpack_relatedposts_filter_date_range', 'jetpackme_related_posts_date_restricted', 10, 2 );