About Rahu Kaal
According to Vedic astrology Rahu is an inauspicious planet. During transition of planets the time under the influence of Rahu should be avoided to do any auspicious work. Doing Puja, Hawan or Yogya to propitiate auspicious planets during this time is interfered by Rahu due to its malefic nature. If one does Puja, Hawan or Yogya during Rahu kaal then desired results are not achieved. Hence it is important to consider Rahu Kaal before starting any new work. By doing so, possibility of achieving desired results is increased.
However any work related to Rahu gives good results during this period. Hawan, Yogya, etc. to propitiate Rahu can be done during this time.