How can I add the order date to the invoice?

Changing format of pdf invoice. How can I add the order date to the invoice? I've been able to edit the template following instructions at https://premium.wpmudev.org/forums/topic/how-to-update-the-pdf-invoices-in-marketpress and edited the file /marketpress/includes/addons/mp-pdf-invoice/templates/invoice.php to include bank info and VAT info. How to include date of order into invoice?