Dear Vivekji, Namaste,
The following link provides us with free calculator for calculating rahu kaal, gulika etc.
http://www.astroccult.net/rahukalam_calculator.html
Let me share some more info regarding the worship of Maa Durga during rahu kaal.
During raghukalam worshipping Durga devi is good. I have seen women litting lemon lamp to Durga in the temples in south India..
"Rahu Kaalam Durga Pooja" is very famous. They are done specially on Tuesdays 3-4:30pm or Fridays 10:30-12noon. Young people who perform this pooja will excel in studies while the unmarried will be able to find a good life partner, married ladies will have a happy married life and their families will proper, the childless will have children and have a happy and prosperous life.
The story behind this Raahu Kaalam Durgra Puja goes like this...
A couple is blessed with a child after their continuous prayers to Mother Durga. The child reached her puberty age and the parents decided to seek an astrologer to ask the fate of the child in future. The couple was shocked to know that their daughter has "Ragu Thosam" (very bad time – Ragu controlling her time ) and the ninth day from her birthday, a black serpent will bite her to death. Hearing this, the couple rushed to get the protection from Mother Durga. Parvathy takes a vow to save the child.
The time comes and as predicted before, Ragu/Rahu (the serpent-head) changes himself as a serpent and try his very best to kill the girl. Each of his attempt been blocked by Shakti and at last Shakti herself reincarnate as the girl and Ragu mistakenly bite Shakti thus made a sinful act. Ragu beg for forgiveness and as a reward he let go the girl. In forgiving his mistakes, Mother Durga tells him that Ragu dosh , Ragu`s influences will ease for those who are performing Pooja for her at Rahu Kaalam (a bad time ) and those who are conducting the pooja will be blessed by Mother Durga.
I heard many saying that it is ideal to start anything auspicious during the last session of raahu kaalam and leads to good result. But Iam not sure it is correct or not.
Regards,