Hola, prueba esto:
<?
$hora1 = '01:00:01' ;
$hora2 = '02:30:59' ;
function sumarHoras($hora1, $hora2) {
$parte1 = explode(":", $hora1);
$h1 = $parte1[0];
$min1 = $parte1[1];
$seg1 = $parte1[2];
$parte2 = explode(":", $hora2);
$h2 = $parte2[0];
$min2 = $parte2[1];
$seg2 = $parte2[2];
$seg = $seg1 + $seg2;
$min = $min1 + $min2;
$hora = $h1 + $h2;
$d = date('d');
$mes = date('m');
$anno = date('Y');
$HoraSumada = date("H:i:s", mktime($hora, $min, $seg, $mes, $d, $anno)) ;
return $HoraSumada;} ;
$hora_actual = sumarHoras($hora1, $hora2);
?>
HORA : <?=$hora_actual?>
Para mas ver:
http://www.hackingballz.com/herramie...tion.date.html