Siman 553

Even though he ate the seuda hamafseket, and he does not intend to eat further, nevertheless if he desired – he is permitted to return and eat, unless he explicitly accepted upon himself not to eat anymore today; for then it is like the acceptance of a fast, and he is forbidden from eating, drinking, and washing. And similarly, if he said: "Behold, I am in a state of fasting for tomorrow" – it is also forbidden (Magen Avraham subsection 1), for perforce its meaning is that he accepts the fast now, for if not so, why does he need to accept it for tomorrow? Is he not already commanded and bound even without his acceptance?

Our teacher, the Rema, wrote in section 1: Acceptance in the heart is not acceptance, but rather one must express it with his lips; thus far his words. And there are those who disagree, that acceptance in the heart is also effective (Bach), and therefore it is good to stipulate at the time of the seuda hamafseket (Magen Avraham, subsection 2) that he does not yet intend to accept the fast. And so too if he thinks thus in his heart, or if this is his usual practice. And such is the common custom among us, that after the seuda hamafseket one may eat and drink if they wish, and every person acts according to the custom.

Tisha B'Av, its night is like its day for all matters, and one only eats while it is still day. Its bein hashemashot is forbidden like Yom Kippur. And even though it is of rabbinic origin—it is not relevant to say "a rabbinic doubt is ruled leniently," since they applied many stringencies to it, regarding washing and the other afflictions. And it is from the words of tradition, which is as stringent as the words of the Torah regarding the matter of bein hashemashot. However, an addition while it is still day is not required like Yom Kippur, and until bein hashemashot, washing, anointing, and wearing leather shoes are permitted. But if he accepted the fast upon himself—it follows that washing and anointing are forbidden, for there is no logic to say that he accepted it halfway, only for eating and drinking. However, regarding wearing leather shoes, if he did not remove them—perforce he did not accept it upon himself (Taz, subsection 1). And when Tisha B'Av falls on a weekday—it is the custom to remove the shoes before "Barchu." And when it falls on the conclusion of Shabbat—only the shaliach tzibbur removes them before "Barchu," and all the people remove them after "Barchu." And they should be careful not to touch the shoes with their hands, so that they will not require washing. And why does the shaliach tzibbur remove them before "Barchu"? So that he will not become confused in his prayer if he removes them after Barchu. And the order of the Kinot will be explained in siman 559.

Our teacher, the Rema, wrote in section 2: It is the custom not to study on the eve of Tisha B'Av from midday onwards, except for those matters that are permitted on Tisha B'Av. Therefore, if it falls on Shabbat—one does not recite Pirkei Avot. Likewise, one should not stroll on the eve of Tisha B'Av; thus far his words. And consequently, if Tisha B'Av falls on Shabbat and is postponed, one should not study the entire day except for those matters that are permitted, for matters of privacy are practiced (Magen Avraham, subsection 7). And some disagree, for since on Shabbat one eats meat and drinks wine—how can we forbid Torah study? Therefore, it is permitted to study the entire day on Shabbat (Taz, subsection 2). And some permit studying on every eve of Tisha B'Av after midday (ibid. in the name of the Rashal), and one may rely on those who are lenient for the sake of preventing the neglect of Torah study. And there is one who wrote: Behold, he is able to study those matters that are permitted (Magen Avraham, subsection 7). But this is not a valid claim, for we see tangibly that once one stops his regular study—he does not study further. (And so wrote the Gra, subsection 9, that it is an excessive stringency, see there). Therefore, one who studies on every eve of Tisha B'Av until nightfall—has not lost his reward. So it appears in my humble opinion.