How many times are listed for 31 May for the rider ranked 5?
CREATE TABLE "practice_times_leaderboard_superstock_tt" (
  "rank" real,
  "rider" text,
  "sat_29_may" text,
  "mon_31_may" text,
  "tues_1_june" text,
  "wed_2_june" text,
  "thurs_3_june" text,
  "fri_4_june" text
);
SELECT COUNT("mon_31_may") FROM "practice_times_leaderboard_superstock_tt" WHERE "rank"=5;