/**
 * @param integer seconds
 * @return string human readable text
 */
function fuzzy_seconds($seconds)
{
    if ($seconds <= 0) return FALSE;

    $w = $seconds / 86400 / 7;
    $d = $seconds / 86400 % 7;
    $h = $seconds / 3600 % 24;
    $m = $seconds / 60 % 60; 
    $s = $seconds % 60;

    $output = array();

    if ($w >= 1) $output[] = "{$w} ".($w == 1 ? 'week' : 'weken');
    if ($d >= 1) $output[] = "{$d} ".($d == 1 ? 'dag' : 'dagen');
    if ($h >= 1) $output[] = "{$h} ".($h == 1 ? 'uur' : 'uren');
    if ($m >= 1) $output[] = "{$m} ".($m == 1 ? 'minuut' : 'minuten');
    if ($s >= 1) $output[] = "{$s} ".($s == 1 ? 'seconden' : 'seconden');

    return implode(', ', $output);
}

Resultaat:

echo fuzzy_seconds(123456);

1 dag, 10 uren, 17 minuten, 36 seconden