Starts somewhere in October or November
Kartik comes after Ashwin month
Deepawali is the last day of Ashwin month. And the first day next to Diwali is the first day of Kartik month.
As per Lunar Calendar, Diwali is Amavasya or No moon day.As per one belief, it is the darkest day of year when negative powers can be most powerful. Hence to anticipate their grip on this day , oil lamps are burnt. As per other beliefs , Lord Rama returned to Ayodhya this day. Hence it is known as Diwali.
Importance of this month as per scriptures - Providing Oil Wick lamps to Lord Krishna. This removes all sins.