Sources describe a new generation of writers and publications (David Foster Wallace, Zadie Smith, McSweeney's and others) as heralding either a new chapter of postmodernism or possibly a distinct post-postmodernism, without resolving which reading is correct, so no consensus end date exists.
What would resolve this A broadly adopted literary-critical consensus, or a landmark critical work, either marking postmodernism's close or confirming its continuation under a new name.
OpenLiterary criticism and periodization scholarshipPostmodern Literature (Wikipedia)