CREATE TABLE table_16505 ("Team" TEXT, "Outgoing manager" TEXT, "Manner of departure" TEXT, "Date of vacancy" TEXT, "Replaced by" TEXT, "Date of appointment" TEXT, "Position" TEXT)

When is the date of vacancy of Davy Fitzgerald being a replacement?
SELECT "Date of vacancy" FROM table_16505 WHERE "Replaced by" = 'Davy FitzGerald'
SELECT "Date of vacancy" FROM "table_16505" WHERE "Replaced by" = 'Davy FitzGerald'