According to the ruling of the Shulhan Aruch, one may not drink milk or eat dairy foods for six hours after eating meat or poultry. An interesting question arises in the case of an exceptionally long meal which extends for over six hours. Consider, for example, the case of a meal on Shabbat that begins with a meat dish at 11:30am. The people at the meal finish their meat dish by noon, and they spend several hours eating salads and side dishes, drinking, singing Pizmonim, and so on. If they still had not recited Birkat Hamazon by 6pm six full hours after they ate meat would it be permissible for them to eat dairy ice cream for dessert?
The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909) writes that this would be forbidden. One may not eat meat and dairy in the same meal, even if he eats them six hours apart from one another. A person who wants to eat dairy foods six hours after eating meat at the same meal must first recite Birkat Hamazon and clear the table before eating the dairy foods.
A different question arises regarding a dairy meal that begins slightly less than six hours after one has eaten meat. For example, a persons six hours end at 6pm, but hes invited to a dairy meal that begins at 5:45pm. Would he be allowed to begin the meal at 5:45pm and eat parve foods, like bread and salad, while refraining from dairy foods until 6pm, when his six-hour waiting period ends? Or, does Halacha forbid beginning a dairy meal within six hours of eating meat, even if one does not eat dairy foods until the six hours end, given the concern that he might mistakenly eat dairy foods before this becomes permissible?
The work Darcheh Teshuba rules that it is permissible to begin a dairy meal before the six hours after meat have concluded. So long as one is careful to ensure that he does not eat anything dairy until the six hours have ended, he may begin the meal and eat only parve foods.
Summary: One may not eat dairy foods at the same meal in which he had eaten meat, even if six hours have passed since he ate meat. If one wishes to eat dairy foods at the same meal, he must first recite Birkat Hamazon and clear the table. It is permissible to begin a dairy meal within six hours of eating meat if one ensures to eat only parve foods and not anything dairy until the six hours have ended.