SELECT COUNT("Date") FROM table_16665 WHERE "Grand Prix" = 'Portuguese Grand Prix'
what of the total number of date where grand prix is portuguese grand prix
CREATE TABLE table_16665 (
    "Round" real,
    "Grand Prix" text,
    "Date" text,
    "Location" text,
    "Pole Position" text,
    "Fastest Lap" text,
    "Winning Driver" text,
    "Winning Constructor" text,
    "Report" text
)