The current text is
Semantics: Returns the number of days between two dates. If StartDate and EndDate are Numbers, this is EndDate – StartDate. If they are both Text, this is DATEVALUE(StartDate) – DATEVALUE(EndDate).
Notice that for Numbers it is EndDate-StartDate, but for Text the other way round.
I have added this to https://github.com/oasis-tcs/odf-tc/issues/35. That way we can track it too for the case we will do an ODF 1.3 errata.
There is a report on [office-comment] mailing list about this, see https://lists.oasis-open.org/archives/office-comment/202311/msg00000.html