CREATE TABLE table_20537 ("Team" TEXT, "Outgoing manager" TEXT, "Manner of departure" TEXT, "Date of vacancy" TEXT, "Replaced by" TEXT, "Date of appointment" TEXT)

When was the date of appointment for St. Johnstone's manager?
SELECT "Date of appointment" FROM table_20537 WHERE "Team" = 'St. Johnstone'
SELECT "Date of appointment" FROM "table_20537" WHERE "Team" = 'St. Johnstone'