According to http://xmpp.org/extensions/xep-0203.html#protocol
the time format should be http://xmpp.org/extensions/xep-0082.html#sect-id2262434
Sometimes the node related has the stamp attribute in a correct format, but sometimes missing the dashes in between the date properties.
So far I haven’t been able to find out the cases when the data would have the correct form.
Um… realised that I was checking out the newer specification for the related functionality.
Actually http://xmpp.org/extensions/xep-0091.html is used, thus the format of the time stamp is mostly correct.
Well now that the subject has surfaced, should the work for updating the code to use http://xmpp.org/extensions/xep-0203.html
as “This specification has been deprecated in favor of Delayed Delivery” is stated in the XEP-0091.