This program will be uses php's STRTOTIME function to get the difference two dates. It will display either in year, month, week, day, hour or minute.

The php function:

function get_ago($minute)
{
    $ago = "";
    if ($minute > 525949 ) {
        $ago = round($minute/525949)." Year Ago";
    } else if ($minute > 43829) {
        $ago = round($minute/43829)." Month  Ago";
    } else if ($minute > 10080) {
        $ago = round($minute/10080)." Week  Ago";
    } else if ($minute > 1440) {
        $ago = round($minute/1440)." Day  Ago";
    } else if ($minute > 60) {
        $ago = round($minute/60)." Hour  Ago";
    } else if ($minute > 0) {
        $ago = round($minute)." Minute  Ago";
    } else {
        $ago = "1 Minute  Ago";
    }
    return $ago;
}

The Calling function:

$to_time = strtotime(date("Y-m-d H:i:s")); //current date
$from_time = strtotime("2012-11-20 20:30:30");
$ago = get_ago(round(abs("$to_time - $from_time") / 60,2));