function CalcHora($hora1,$hora2)
   {
			$hh=explode(":",$hora1);
			$hhh=explode(":",$hora2);
			$ho=round($hh[0]*60);
			$totale=$ho+$hh[1];
			$hoo=round($hhh[0]*60);
			$totals=$hoo+$hhh[1];
			$t=$totals-$totale;
			$t=round($t/60,4);
			$t=explode(".",$t);
			$tt='.'.$t[1];
			$tr=round($tt*60,2);
			$resposta=$t[0].':'.$tr;
	
	return $resposta;
   } 
   $hora1="22:00";
   $hora2="30:00";
echo function CalcHora($hora1,$hora2);
//imprimira 8:00