If you need specific formatting for the date shown on your QWeb report, you can achieve that by defining the attribute t-field-options with value {“format”: “<formating type>”}
For example, if you need the Invoice Date to be shown as 14.11.2016 the code would look like:
<span t-field="o.date_invoice" t-field-options='{"format": "%d.%m.%Y"}'/>
For me (version 11)
t-options='{“widget”: “date”, “format”: “dd/MM/yyyy”}’