echo getTimeDiff("10:30","11:10");

function getTimeDiff($dtime,$atime)
    {
        $nextDay = $dtime>$atime?1:0;
        $dep = explode(':',$dtime);
        $arr = explode(':',$atime);
        $diff = abs(mktime($dep[0],$dep[1],0,date('n'),date('j'),date('y'))-mktime($arr[0],$arr[1],0,date('n'),date('j')+$nextDay,date('y')));
        $hours = floor($diff/(60*60));
        $mins = floor(($diff-($hours*60*60))/(60));
        $secs = floor(($diff-(($hours*60*60)+($mins*60))));
        if(strlen($hours)<2){$hours="0".$hours;}
        if(strlen($mins)<2){$mins="0".$mins;}
        if(strlen($secs)<2){$secs="0".$secs;}
        return $hours.':'.$mins.':'.$secs;
    }

$monday = date( 'Y-m-d', strtotime( 'monday this week' ) );
$friday = date( 'Y-m-d', strtotime( 'friday this week' ) );