Is Ashtami and Navami on the same day?

In Sandhi Puja, the last 24 minutes of Ashtami and the starting 24 minutes of Navami are called as Sandhi time or Kaal. The time of Sandhi Kaal is considered as the most auspicious time for Durga Puja. Because it is this time only when Ashtami Tithi ends and Navami Tithi begins.
Why do some people celebrate Ashtami and some Navami?

One of the many reasons why this festival is widely celebrated is to receive the blessings of the Goddess with the aim of being granted wealth, prosperity, as well as knowledge. Every festival celebrated in India has a profound attachment and significance with buying investments in the form of gold, silver, and properties.
Is Ashtami good or Navami?

Nowhere in the sastras, it was mentioned that Ashtami and Navami are called bad luck days. In fact, these things are auspicious if there is a strong muhurta for marriages and housewarming ceremonies.
What is meant by Navami?

Navami is the Sanskrit word for “nine”, and is the ninth day in the lunar fortnight (Paksha) of the Hindu calendar. Each month has two Navami days, the ninth day of the “bright” (Shukla) and of the “dark” (Krishna) fortnights respectively. Thus Navami occurs on the ninth and the twenty-fourth day of each month.