relative_timestamp.php

<?php
function ago($time)
{
    $time = strtotime($time);
    $periods = array("second", "minute", "hour", "day", "week", "month", "year", "decade");
    $lengths = array("60", "60", "24", "7", "4.35", "12", "10"); 

    $now = time(); 

    $difference = $now - $time;
    $tense = "ago"; 

    for ($i = 0; $difference >= $lengths[$i] && $i < count($lengths) - 1; $i++) {
        $difference /= $lengths[$i];
    } 

    $difference = round($difference); 

    if ($difference != 1) {
        $periods[$i] .= "s";
    } 

    return "$difference $periods[$i] ago ";
}
?>