A person does not fulfill the obligation of Kiddush on Shabbat unless he either eats a Kezayit of bread or Mezonot food, or drinks a Rebi段t of wine, after reciting or hearing Kiddush. One is required to partake of the food or wine immediately after Kiddush, without any delay. It is improper to delay eating after hearing Kiddush, since the Kiddush must be recited within the context of a meal.
If a person did delay eating or drinking wine, and did not eat or drink immediately after the Kiddush, he has nevertheless fulfilled his obligation and does not have to repeat Kiddush. The exception to this rule is a case where one had in mind when he recited Kiddush that he would eat only 72 minutes or more after Kiddush. If a person from the outset planned on delaying eating for this amount of time, he has not fulfilled the Misva of Kiddush and must recite Kiddush again. But if somebody intended to eat immediately after Kiddush and then something came up and resulted in a delay, he has fulfilled his obligation. Even though one should certainly make an effort to eat or drink immediately after Kiddush, he fulfills his obligation so long as he had not planned from the outset to delay eating or drinking. This is the ruling of Hacham Ovadia Yosef, in his work Halichot Olam (vol. 3, p. 3; listen to audio recording for precise citation).
Summary: One must eat a Kezayit of bread or Mezonot food, or drink a Rebi段t of wine, immediately after reciting or hearing Kiddush, without delay. One who delayed eating or drinking has nevertheless fulfilled his obligation of Kiddush, provided that he had not planned from the outset to delay eating or drinking for 72 minutes or more.
