CREATE TABLE table_21487 ("Week" FLOAT, "Date" CLOB, "Opponent" CLOB, "Result" CLOB, "Game site" CLOB, "Record" CLOB, "Attendance" FLOAT)

When did the Broncos play the Miami Dolphins?
SELECT "Date" FROM table_21487 WHERE "Opponent" = 'Miami Dolphins'
SELECT "Date" FROM "table_21487" WHERE "Opponent" = 'Miami Dolphins'