CREATE TABLE table_3309 ("Circuit" TEXT, "Location" TEXT, "Date" TEXT, "Series" TEXT, "Winning driver" TEXT, "Winning team" TEXT)

When was the F4 7 series?
SELECT "Date" FROM table_3309 WHERE "Series" = 'F4 7'
SELECT "Date" FROM "table_3309" WHERE "Series" = 'F4 7'