In which month are the eight days referred to in the Almighty’s saying: "and eight days in succession"? And is it true what some elders say, that conception during these days may result in birth defects?

There is disagreement regarding the specific days on which Allah destroyed 'Ad. It has been said that it began on a Sunday, or a Friday, or a Wednesday. These days are called "Ayyam al-'Ajuz" (Days of the Old Woman), either because they are attributed to an old woman from 'Ad who was killed by the wind during them, or because they fall at the end (ajuz) of winter. They occur in March or the end of February. As for what is rumored about deformities affecting anyone conceived by their mother during these days, that is incorrect. These days were a punishment for the people of 'Ad alone.