$start // начало отсчета
$today = time(); // конец
$round = $today - $start; // промежуток
$chas = round($round/3600); // сколько часов прошло

<?php  
function removeTime($mytime){  
$limit = time()-$mytime;  
if($limit>(3600*24*30)){  
$mounth = round($limit/(3600*24*30));  
$limit = $limit - ($mounth*3600*24*30);  
$remove = $mounth.' Mounth. ';  
}  
if($limit>(3600*24)){  
$day = round($limit/(3600*24));  
$limit = $limit - ($day*3600*24);  
$remove. = $day.' days. ';  
}  
if($limit>3600){  
$hour = round($limit/3600);  
$limit = $limit - ($hour*3600);  
$remove. = $hour.' hours. ';  
}  
return $remove;  
}