CREATE TABLE table_65623 ("Circuit" TEXT, "Date" TEXT, "Pole Position" TEXT, "Fastest Lap" TEXT, "Winning driver" TEXT, "Winning team" TEXT)

What date was the circuit, snetterton, when riki christodoulou had the fastest lap?
SELECT "Date" FROM table_65623 WHERE "Circuit" = 'snetterton' AND "Fastest Lap" = 'riki christodoulou'
SELECT "Date" FROM "table_65623" WHERE "Circuit" = 'snetterton' AND "Fastest Lap" = 'riki christodoulou'