Laws of Public Fast Days
8. There is a difference between the first three fasts mentioned (1) and
Tish'ah B'Av. On the first three fasts, one may eat on the night before
the fast until dawn provided one did not sleep for an extended period
beforehand. If, however, one did sleep for an extended period, one is
forbidden to eat or drink upon rising, [even if it is before dawn], unless
one made an explicit stipulation to that effect before going to sleep. If
one is accustomed to drinking after sleep, it is unnecessary to make a
stipulation about drinking.
In contrast, on Tish'ah B'Av, one must stop eating and drinking before
sunset (on the previous day). Also, on the first three fast days, washing
oneself with water, anointing oneself with oil, wearing [leather] shoes,
and marital relations are permitted, while on Tish'ah B'Av all these
activities are forbidden (2).
[Nevertheless,] a "Baal Nefesh" (3) who is healthy, should be stringent and
[refrain from all these activites] on the other fast days as on Tish'ah
B'Av; however, one should not be stringent regarding wearing leather shoes,
because one might become the object of ridicule. If [one's wife] has to
immerse in the mikveh during the evening [before] one of the first three
fasts, one should fulfill one's obligation of engaging in marital relations
("onah") [on that night] (4).
(1) Tzom Gedaliah, Asarah Be'Teves, and Shiva Asar Be'Tamuz.
(2) When the Jewish people accepted these four public fasts upon
themselves, they did not accept the stringencies of Tish'ah B'Av for the
others three fasts (Mishna Berura 550:6).
(3) This term is hard to translate; generally it refers to someone who
feels that they are on the level to go beyond the letter of the law.
(4) Since marital relations had been forbidden for a certain period before
one's wife immersed in the mikvah, it is a mitzvah to engage in marital
relations immediately after the immersion.