<?
$a="2200";
$b="0430";

function GetTotalTime($a,$b) {
$hh1 = substr('$a', 0, 2);
$hh2 = substr('$b', 0, 2); 
$mm1 = substr('$a', 2, 2);
$mm2 = substr('$b', 2, 2);

if($hh1>$hh2) {

$hh_between = 24 - $hh1 + $hh2;

}
else {

$hh_between = $hh2 - $hh1;

}

if($mm1>$mm2) {

$mm_between = 60 - $mm1 + $mm2;

}
else {

$hh_between = $hh2 - $hh1;

}
}

$totaltime=GetTotalTime($a,$b);
echo $totaltime;
?>