TIL that, at least according to the linked page, YYYY-MM-DD hh:mm:ss (or %Y-%M-%D %h:%m:%s in strftime format) isn't valid in either system.

ISO8601 apparently disallows spaces altogether, so that space should be a T for it to qualify there; RFC3399 allows the space, but insists there should be a UTC offset of some kind at the end.

Unrelatedly, the page's use of %Z and %z doesn't match with strftime formatting at all, so there's at least one other standards problem lurking here.