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

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'