Вот, например, в друпале, делают так:
format_interval(time() - $timestamp)
где function format_interval
Format a time interval with the requested granularity.
Parameters:
$timestamp The length of the interval in seconds.
$granularity How many different units to display in the string
function format_interval($timestamp, $granularity = 2) {
$units = array('1 year|%count years' => 31536000, '1 week|%count weeks' => 604800, '1 day|%count days' => 86400, '1 hour|%count hours' => 3600, '1 min|%count min' => 60, '1 sec|%count sec' => 1);
$output = '';
foreach ($units as $key => $value) {
$key = explode('|', $key);
if ($timestamp >= $value) {
$output .= ($output ? ' ' : '') . format_plural(floor($timestamp / $value), $key[0], $key[1]);
$timestamp %= $value;
$granularity--;
}
if ($granularity == 0) {
break;
}
}
return $output ? $output : t('0 sec');
}