CREATE TABLE table_55040 ("Home team" TEXT, "Home team score" TEXT, "Away team" TEXT, "Away team score" TEXT, "Venue" TEXT, "Crowd" FLOAT, "Date" TEXT)

On what Date did the Away team essendon play?
SELECT "Date" FROM table_55040 WHERE "Away team" = 'essendon'
SELECT "Date" FROM "table_55040" WHERE "Away team" = 'essendon'