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It is well known that people lighto shabbas candles before(many are careful to light 18-20 minutes before) shikya and no later. However, the Kitzur Shulchan Aruch 75:1 holds one has until 30 minutes before the emergence of 3 medium stars. So in a pressing situation why cant one hold like the Kitzur Shulchan Aruch? I have seen poskim who write that after shekiya it is forbidden (Mishna Brurah) and discuss if a non-Jew can light in their stead (Biur Halacha).