#Although it is forbidden to begin eating after sunset until one says havdala, <ref> Shulchan Aruch 291:1 </ref> and it is definitely preferable to eat before sunset, some poskim give extra time to begin the meal if one hasn't yet eaten seuda shlishit.
*Mishna Berura 299:1 says that if one hasn't yet eaten the meal or is really starving then one can still eat until a half hour before tzet hakovachim.
*Pninei Halacha [[Shabbat]] vol. 1 page 130 quotes Rav Moshe Feinstein Iggerot Moshe 4:69:6
and Yalkut Yosef 291:20 that one has until thirteen minutes and a half minutes after sunset.
#If one began eating before sunset he may continue after. <ref> Shulchan Aruch 299:1, Aruch Hashulchan 299:3. Mishna Berura 291:2 says that having said the beracha is enough of a start to your meal to allow one to continue afterwards. He also quotes an opinion that this only applies during bein hashemashot but after tzet hakochavim one would not be allowed to continue. Rama says that the minhag is not so, rather one can continue even after tzet hakochavim, and the aruch hashulchan 299:4 says that is the minhag. </ref> However, this doesn't apply if one was only drinking not as part of a meal <ref> Shulchan Aruch 299:1 </ref> or to eating only mezonot or fruit, so one must stop if that is all that he is having. <ref> Aruch Hashulchan 299:5 </ref>