Table schema:
CREATE TABLE table_name_67 (date VARCHAR, sample_size VARCHAR, democrat VARCHAR, republican VARCHAR, poll_source VARCHAR)

Question: What is the date that the polls were going on at quinnipiac when john mccain was the republican, barack obama was the democrat and the sample size was bigger than 1427?
SQL: SELECT date FROM table_name_67 WHERE republican = "john mccain" AND poll_source = "quinnipiac" AND democrat = "barack obama" AND sample_size > 1427