Biswakarma puja is annually scheduled on the last day of the Bengali month of Bhadra, more specifically on Bhadra sankranti. That is when the sun transits from Singha (Leo) to Kanya (Virgo) sign.
The festival is mainly celebrated in Bengal, Orissa and Tripura. It is a holiday for the industrial belts in this part of India. Kite flying is a major activity on the day.
In Hindu Mythology, Vishwakarma is the divine architect of the universe. He is also called the divine carpenter and is mentioned in the Rig Veda and is credited with Sthapatya Veda, the science of mechanics and architecture.