The blessing of Leisheiv Bassukah
When is the blessing of Leisheiv said? The blessing of ‘Leishev Basukkah’ is only said when eating a Kebeitza [55 grams] of Mezonos or Hamotzi [within Achilas Peras]. It is not said prior to other actions of dwelling such as a set drinking session, or spending time of leisure or sleeping in the Sukkah.
Is the blessing of Leisheiv Basukkah said before or after the blessing over food? The blessing of Leisheiv is recited after saying the blessing of the food, but prior to eating it. Thus if one eats bread he first says Hamotzi and then say Leisheiv and then eat. If he is eating a Kibeitza of Mezonos he first says Mezonos, then Leishev and then eats the Mezonos. [The Rebbe’s custom is to look at Sechach upon saying Leisheiv.]
How often does one say the blessing of Leishev over eating in a Sukkah: Every time one eats a Kebeitza of Mezonos or Hamotzi in the Sukkah he is to say a blessing of Leisheiv Bassukah, if there was an interval between the previous time he ate and the current eating. If however no interval was made then he does not repeat the blessing, as the previous blessing still covers his current eating. This applies even if one remained in the Sukkah throughout all seven days of Sukkos without an interval, in which case he would only say the blessing on the first meal he eats in the Sukkah. The definition of an interval is either intent or time. This means as follows: If one left the Sukkah after eating and had intent to not return within one to two hours then even if he returns immediately he must repeat the blessing prior to eating a Kibeitza of Mezonos. Likewise even if one intended to return within one to two hours, but in actuality returned after one to two hours, then it is considered an interval and he must repeat the blessing prior to eating a Kibeitza of Mezonos.
Must one repeat the blessing of Leishev Basukah when eating in a second Sukkah? One must say the blessing of Leisheiv in every Sukkah that he eats a Kibeitza of Mezonos. This applies even if he had in mind to eat in the second Sukkah at the time he began eating in the first Sukkah, and applies even if both Sukko’s are next to each and a new first blessing is not required to be repeated, nevertheless a new blessing must be said.
Saying the blessing of Leishev on simply relaxing or sleeping in someone else’s Sukkah: If one enters into someone else’s Sukkah in order to spend time of leisure, or in order to sleep in it, and he does not plan to eat a Kibeitza worth of Mezonos in that Sukkah then he must say the blessing of Leishiev Basukkah prior to relaxing or sleeping in it. However, if one plans on eating a Kibeitza of Mezonos in that Sukkah, or if he already ate a Kibeitza there, then these acts are exempt with the blessing made on the food.
If one forgot to say Leisheiv before eating: If one forgot to recite Leisheiv Basukkah prior to eating he is to say it upon remembering. If he has already finished eating and then remembered to say the blessing, then if he is still in the Sukkah he is to say the blessing upon remembering [even if he has already Bentched].
What is the law if one left the Sukkah without any intent and returned within one to two hours?
Example: If one left the Sukkah to take a walk without intent to return or not return, if he returned does he repeat the blessing?
Seemingly so long as one did not intend to not return within 2 hours it is valid. Meaning if one did not intend anything before leaving then if he returns within 2 hours it is valid, and only when he specifically has intent to not return must he say another blessing.
 The reason: The reason for this is because the blessing of Leisheiv which is said over food covers all acts of dwelling that one does in the Sukkah. This applies even if one will be eating after these forms of dwelling as these acts are secondary and included in the future blessing. The reason for why the blessing is only said on food is because eating food in the Sukkah is the main Mitzvah of dwelling in the Sukkah. [ibid]
 From the letter of the law it is proper to say the blessing of Leisheiv before Hamotzi as one becomes obligated in the blessing as soon as he sits down to eat even prior to eating. Nevertheless the custom is to say the blessing after Hamotzi as the custom is to only say Leisheiv on a meal and hence we first say Hamotzi which is the start of the meal and only after do we say Leisheiv. This blessing is not considered a Hefsek between the blessing of Hamotzi and the eating being that this blessing is needed for the meal and any matter which is needed for the meal is not considered an interval. [ibid]
 This implies that so long as one did not intend to not return within 2 hours it is valid. Meaning if one did not intend anything before leaving then if he returns within 2 hours it is valid, and only when he specifically has intent to not return must he say another blessing. [ibid]
 Such as one switched Sukkos after eating a Kezayis of bread or Mezonos.
 639/15; So brings also Hiskashrus 949 p. 12
 The reason: As although all blessings must be said prior to the Mitzvah, nevertheless here since also the sitting in the Sukkah, which he is doing after eating, is also part of the Mitzvah therefore he may still say the blessing, as it is considered as if he is blessing prior to the Mitzvah. [ibid] The M”B 639/48 adds that one is to eat a small amount after saying the blessing prior to Bentching. Admur does not mention this detail.
 M”B 639/48