CREATE TABLE table_13685 ("Date" TEXT, "Tournament" TEXT, "Winning score" TEXT, "Margin of victory" TEXT, "Runner ( s ) -up" TEXT)

What date was there a playoff on the margin of victory during the Shirley Englehorn Invitational?
SELECT "Date" FROM table_13685 WHERE "Margin of victory" = 'playoff' AND "Tournament" = 'shirley englehorn invitational'
SELECT "Date" FROM "table_13685" WHERE "Margin of victory" = 'playoff' AND "Tournament" = 'shirley englehorn invitational'