Add value (Array) in database - php

Question

I tried this code but it does not work for me. i just want to add the array value to database. it give me error like this
Notice: Undefined offset: 2
Here is my code:
$timeadd = date("m-d-Y H:i:s", strtotime('+6 hours'));
$extinvoice=mysqli_query($link,"Select * from invoice WHERE BRANCH_CODE_MX='".$display_branchcode."' and INVOICE_NO_MX='".$invoicecode."' and INVOICE_ITEM_UNIT_MX='EXTENDEDWARRANTY'");
while($extrow=mysqli_fetch_array($extinvoice))
{
$ewtitemcode=$extrow["INVOICE_ITEM_CODE_MX"];
$imeiserialunit=$extrow["EWT_IMEI_MX"];
$customercode=$extrow["INVOICE_CUS_CODE_MX"];
$ewtarray[] = "('$invoicecode','$ewtitemcode', '$imeiserialunit','$customercode','$display_branchcode','$timeadd')";
}
$arrayitem=count($ewtarray);
for($item = 0; $item <= $arrayitem; $item++)
{
$sql = mysqli_query($link,"INSERT INTO extended_warranty
(INVOICE_NO_MX,FORM_EW_MX,EW_SERIAL_MX,CUSTOMER_CODE,BRANCH_CODE_MX,DATE_ADDED)
VALUES
($ewtarray[$item])");
}

Answer 1

The database requires a datatime in the format
2016-10-02 10:00:00
So change this
$timeadd = date("m-d-Y H:i:s", strtotime('+6 hours'));
to
$timeadd = date("Y-m-d H:i:s", strtotime('+6 hours'));

Answer 2

Additionally to the other users I have removed the double brackets. What happens now?
$timeadd = date("Y-m-d H:i:s", strtotime('+6 hours'));
$extinvoice=mysqli_query($link,"Select * from invoice WHERE BRANCH_CODE_MX='".$display_branchcode."' and INVOICE_NO_MX='".$invoicecode."' and INVOICE_ITEM_UNIT_MX='EXTENDEDWARRANTY'");
while ($extrow=mysqli_fetch_array($extinvoice)) {
$ewtitemcode=$extrow["INVOICE_ITEM_CODE_MX"];
$imeiserialunit=$extrow["EWT_IMEI_MX"];
$customercode=$extrow["INVOICE_CUS_CODE_MX"];
$ewtarray[] = "('$invoicecode','$ewtitemcode', '$imeiserialunit','$customercode','$display_branchcode','$timeadd')";
}
for ($item = 0; $item < count($ewtarray); $item++) {
$sql = mysqli_query($link,"INSERT INTO extended_warranty
(INVOICE_NO_MX,FORM_EW_MX,EW_SERIAL_MX,CUSTOMER_CODE,BRANCH_CODE_MX,DATE_ADDED)
VALUES
$ewtarray[$item]");
}