Why do my dates not display on this graph (drupal, php, mysql)?

Why do my dates not display on this graph (drupal, php, mysql)?

My mission this week has been to create a sales graph for my Drupal 6,
Ubercart and Ubercart Marketplace installation.
I settled on the charts_graphs module and decided to use the Bluff library
to graph the data. Although the supported module views_charts allows you
to create a wide range of charts, it wasn't able to retrieve the dataset
that I needed to graph the sales data. If anyone wants the details of why
not, just ask and I'll do my best to elaborate.
So I found an example of the php needed to generate a bluff graph:
<?php
$canvas = charts_graphs_get_graph('bluff');
$canvas->title = "Bluff Chart";
$canvas->type = "line"; // a chart type supported by the charting
engine. See further in the doc for the list.
$canvas->y_legend = "Y Legend";
$canvas->colour = '#D54C78';
$canvas->theme = 'keynote';
$canvas->series = array(
'Some Value' => array(9,6,7,9,5,7,6,9,7),
'Page Views' => array(6,7,9,5,7,6,9,7,3),
);
$canvas->x_labels = array('one', 'two', 'three', 'four', 'five',
'six', 'seven', 'eight', 'nine');
$out = $canvas->get_chart();
return $out;
}
?>
This code then generates this graph...

The next stage of course is to get the data from a MySQL query into the
graph. This is where I'm outside of my comfort zone because I haven't
really done anything previously with PHP.
So after some digging around I found this post with an example that gave
me something to work with. I then used views to help get me started with
the SQL. I'm so close I can taste it but this last issue has had me
snagged and I can't think of any more searches to do... I'm sure you can
relate with that feeling :)
So this is the code I've developed so far:
<?php
global $user;
$uname = $user->uid;
$sql = "SELECT DATE_FORMAT((FROM_UNIXTIME(uc_orders.created) + INTERVAL
3600 SECOND), '%d/%m/%Y') as OrderDate, round(SUM(uc_order_products.cost *
uc_order_products.qty),2) AS SellerCommission,
round(SUM(uc_order_products.price * uc_order_products.qty),2) AS
CustomerPrice
FROM uc_order_products
LEFT JOIN node node_uc_order_products ON uc_order_products.nid =
node_uc_order_products.nid
LEFT JOIN uc_orders uc_orders ON uc_order_products.order_id =
uc_orders.order_id
INNER JOIN users node_uc_order_products__users ON
node_uc_order_products.uid = node_uc_order_products__users.uid
WHERE (node_uc_order_products__users.uid = $uname )
AND (uc_orders.created >= UNIX_TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL
DAYOFMONTH(CURDATE())-1 DAY)))
AND (uc_orders.order_status in ('payment_received', 'completed'))
GROUP BY DAY(FROM_UNIXTIME(uc_orders.created))
ORDER BY MONTH(FROM_UNIXTIME(uc_orders.created)) desc,
DAY(FROM_UNIXTIME(uc_orders.created)) desc
LIMIT 31";
$result = db_query($sql,$uname);
while($row = db_fetch_array($result))
{
$sellercommission[] = (int) $row[SellerCommission];
$customerprice[] = (int) $row[CustomerPrice];
$orderdate[] = (string) $row[OrderDate];
}
$canvas = charts_graphs_get_graph('bluff');
$canvas->title = "Volume of sales";
$canvas->type = "line"; // a chart type supported by the charting
engine. See further in the doc for the list.
$canvas->y_legend = "Y Legend";
$canvas->colour = '#FFFFFF';
$canvas->width = '450';
$canvas->height = '300';
$canvas->theme = '';
$canvas->series = array(
'Seller Commission' =>array_values($sellercommission),
'Customer price' =>array_values($customerprice),
);
$canvas->x_labels = array_values($orderdate);
$out = $canvas->get_chart();
return $out;
?>
This code generates a perfect graph, all but the x-axis only displays "//"
for the dates...

When I run the query on the database this is the result set that I get.
Obviously I replace the placeholder with a UID:
09/09/2013 1328.13 1897.32
07/09/2013 455.00 650.00
What I can't work out is the type for "$orderdate[] ...." that I should be
using. I've tried varchar, int (displays 0), date (breaks it and displays
nothing), datetime (breaks it again)... Or perhaps I am retrieving the
wrong data as OrderDate in the SQL. Any ideas would be greatly
appreciated...