CREATE TABLE table_450 ("Character ( s ) " TEXT, "First Appearance" TEXT, "Cover Date" TEXT, "Publisher" TEXT, "Estimated Value" TEXT)

what's the cover date where character(s) is x-men ; magneto
SELECT "Cover Date" FROM table_450 WHERE "Character(s)" = 'X-Men ; Magneto'
SELECT "Cover Date" FROM "table_450" WHERE "Character(s)" = 'X-Men ; Magneto'