10 instances in the Iliad, where it refers to Achaea Phthiotis in Thessaly, and not to Greece in general.
Wikipedia (Names of the Greeks) is reasonably sure that Hellen, after whom the Hellenes are named, is a Just-So origin myth, and that the more general use of Hellas dates from the Great Amphictyonic League, the first alliance of Greek poleis—which included Thessaly.
In Greek mythology, Hellen, the patriarch of Hellenes, was son of Deucalion, who ruled around Phthia with Pyrrha, the only survivors after the great deluge. It seems that the myth was invented when the Greek tribes started to separate from each other in certain areas of Greece and it indicates their common origin. The name Hellenes was probably used by the Greeks with the establishment of the Great Amphictyonic League. This was an ancient association of Greek tribes with twelve founders which was organized to protect the great temples of Apollo in Delphi (Phocis) and of Demeter near Thermopylae (Locris). According to legend it was founded after the Trojan War, by the eponymous Amphictyon, brother of Hellen.