Warning: mktime() expects parameter 1 to be long, string given in xxxxxx

[beppewhyte]

Buongiorno a tutti,
ho il sito in locale con su xampp e avrei un problema che mi dà questo errore ma non riesco a individuare dove effettuare la modifica:

Warning: mktime() expects parameter 1 to be long, string given in C:\xampp\htdocs\include\funzioni.inc.php on line 583

la funzione è questa:

  function operation($operator,$date,$operand)
    {
        $ts = mktime("", "", "", substr($date,3,2), substr($date,0,2), substr($date,6,4));

        $t=explode('%',$operand);
        $how=$t[0];

        switch($t[1])
        {
            case 'D':
            {
                if($operator=='+' || $operator=='sum' || $operator=='add')
                {
                    return date("d/m/Y",mktime(0,0,0,date('m',$ts),date('d',$ts)+$how,date('Y',$ts)));
                }
                elseif($operator=='-' || $operator=='sub' || $operator=='sot')
                {
                    return date("d/m/Y",mktime(0,0,0,date('m',$ts),date('d',$ts)-$how,date('Y',$ts)));
                }
                break;
            }
            case 'M':
            {
                if($operator=='+' || $operator=='sum' || $operator=='add')
                {
                    return date("d/m/Y",mktime(0,0,0,date('m',$ts)+$how,date('d',$ts),date('Y',$ts)));
                }
                elseif($operator=='-' || $operator=='sub' || $operator=='sot')
                {
                    return date("d/m/Y",mktime(0,0,0,date('m',$ts)-$how,date('d',$ts),date('Y',$ts)));
                }
            }
            case 'Y':
            {
                if($operator=='+' || $operator=='sum' || $operator=='add')
                {
                    return date("d/m/Y",mktime(0,0,0,date('m',$ts),date('d',$ts),date('Y',$ts)+$how));
                }
                elseif($operator=='-' || $operator=='sub' || $operator=='sot')
                {
                    return date("d/m/Y",mktime(0,0,0,date('m',$ts),date('d',$ts),date('Y',$ts)-$how));
                }
                break;
            }
        }
    }

alla riga segnalata, cioè la 583 c'è scritto questo:

  $ts = mktime("", "", "", substr($date,3,2), substr($date,0,2), substr($date,6,4));

Potete aiutarmi per cortesia ?
Vi ringrazio anticipatamente
Beppewhyte