Rahu Kaal, Gulika, and Yamaganda are three daily 'poisonous' time segments during daylight hours that completely block the success of any action.
Poisonous days in astrology.
1 min to readI'd like to know whether it's worth paying attention to this when starting magical work
I seriously doubt that makes sense. Vedic astrology has been shown on several occasions to be not entirely reliable.
Such important and impactful information would have been posted in the ToZ in the appropriate section.