Winter Rye (cover crop) is classed hardy in the cited extension guidance. The timing rules below are relative to your local freeze dates — enter a location to turn them into calendar dates.
The rules this site applies
Method
Frost-relative window
Rule & reconciliation
Fall planting
30–16 days before the median first fall freeze
UMass Extension's cover-crop fact sheet sets the general rule at about 30 days before the first expected frost date and, in the following sentence, names winter rye as a species that may go in a little closer to that date; the stated 30-day point is taken as the window opening and expanded to the standard 14-day span, with rye's tolerance for later seeding noted rather than quantified, since "a little closer" prints no number.
Variety assumption: Assumes seeding for overwintering ground cover with most growth resumed in early spring, then turned under before the next crop.