Navaratri and Gupt Navaratri - Solar Days or Lunar Phases?

E.g. Drikpanchang is showing me the beginning of Chaitra Navaratri this year on 30 March, then Dwitiya and Tritiya both fall on 31st, Chaturthi on 1st April. So Maa Chandraghanta (3rd day) would be worshiped on 31st or 1st?