Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_49930 ( "Game" real, "Date" text, "Opponent" text, "Result" text, "Bills points" real, "Opponents" real, "Bills first downs" real, "Record" text, "Attendance" real )

### Question ###
Which date did the oakland raiders play as the opponent when the Bills first downs were under 28?

### Accurate SQL ###

SELECT "Date" FROM table_49930 WHERE "Bills first downs" < '28' AND "Opponent" = 'oakland raiders'