See: Diwali Muhrat Time 2011 This year Deepawali is on 26th October, 2011. A very large section of the Hindu society depends on astrology and adheres to the ideal time (muhurats) to perform the pujas and invest.

Diwali in 2011 will start on Wednesday, the 26th of October and will continue for 5 days until Sunday, the 30th of October.
 
Diwali is celebrated in late Ashwin (September–October) and ends in early Kartika (October–November).