Halacha requires drinking four cups of wine at the Seder, and each cup must contain at least a Rebi’it – approximately 3.2 ounces – of wine. Preferably, one should drink the entire cup, but one fulfills his obligation even if he drinks less, as long as he drinks at least the majority of the cup (Shulhan Aruch Orah Haim 472:8).
The question arises, in what time-frame must one drink this amount in order to be considered to have drunk a cup of wine? Within how much time one must drink the Rebi’it (or the majority of the cup)?
The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), in several contexts, maintains that one is considered to have drunk a Rebi’it if he drinks it within the amount of time that is normally needed to drink this amount. This is, of course, a very short period of time. According to the Rambam, then, it would seem that when drinking each of the four cups, one must drink the Rebi’it all at once. The Ra’abad (Rabbi Abraham Ben David of Posquieres, 1125-1198), however, disagrees, and maintains that one is considered to have drunk a Rebi’it if he drinks this amount within the period of "Kedeh Achilat Paress," which is defined as anywhere from four minutes to nine minutes. This view is based on the Gemara’s discussion in Masechet Keritut (13). The Shulhan Aruch, in discussing the laws of Yom Kippur (Orah Haim 612:10), appears to follow the Rambam’s view, as he writes that one violates the prohibition of drinking on Yom Kippur if he drinks a Rebi’it in the amount of time normally needed to drink this quantity. Elsewhere in the laws of Yom Kippur, however, in discussing the guidelines for ill patients, the Shulhan Aruch indicates that he follows the Ra’abad’s view. Thus, the Shulhan Aruch’s position on this issue is unclear.
When it comes to the laws of Berachot, the accepted practice is not to recite a Beracha Aharona after drinking unless one drank a Rebi’it all at once and is thus required to recite a Beracha Aharona even according to the Rambam. In light of the rule of "Safek Berachot Le’hakel" – we do not recite a Beracha in situations of uncertainty – we do not recite a Beracha Aharona unless a Rebi’it was drunk all at once, within the time normally needed to drink this amount, in deference to the Rambam’s position.
Returning to the four cups of wine at the Seder, Hacham Ovadia Yosef, in his Hazon Ovadia – Teshubot, rules that although one should preferably drink the cup all at once, if this is difficult one may rely on the Ra’abad’s view. He writes that since the obligation of Arba Kosot (the four cups) was enacted by the Sages, and does not constitute a Biblical requirement, one may rely on those authorities who allow drinking the required amount within the period of "Kedeh Achilat Paress." Although the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Sav (29), maintains that one who did not drink the required amount all at once must drink another cup, Hacham Ovadia disagrees. In his view, although one should preferably drink the required amount all at once, if one drank within 4-9 minutes he has fulfilled his obligation. This is the position taken by several other Halachic authorities, as well, including the Aruch Ha’shulhan, Rav Haim Palachi and Hacham Bension Abba Shaul.
It should be noted that one does not have to drink the required amount in a single gulp. Even according to the Rambam’s view, the Rebi’it must be drunk within the time-frame that is normally needed to drink this amount, and therefore, as it is normal for people to drink in two gulps, this would be perfectly acceptable.
See shaar ha siyun 210 sk 11
Summary: Each of the four cups of wine at the Seder must contain at least 3.2 ounces of wine, and one should preferably drink the entire cup all at once, without pausing, though it does not have to be drunk in a single gulp. If it would be difficult to drink the entire cup, one should drink at least the majority of the cup. If it would be difficult to drink the required amount all at once, it may be drunk within a period of 4-9 minutes.
