The Be’er Heteb commentary to the Shulhan Aruch (Eben Ha’ezer 26:4) writes that if a Kiddushin (betrothal) ceremony is performed at night, it is uncertain whether it is valid. The basis for questioning the validity of nighttime wedding ceremonies is the view of the Re’em, cited in the work Pit’heh Teshuba, who held that Kiddushin must be performed during the daytime just as a Get – according to some authorities – may be given only during the day. In many places in the Talmud, we find a principle called "Makish Havaya Le’yesi’a" – literally, "we compare creating marriage to leaving marriage" – which means that the laws of Kiddushin and those of divorce are similar to one another. Giving a Get, according to some authorities, must be done during the day, because the process of divorce entails the resolution of financial issues – specifically, the husband’s payment of the Ketuba – and judicial proceedings of a Bet Din are conducted only during the day. By the same token, the Re’em held, Kiddushin, which is comparable to divorce, must take place only during the day. This position is also cited in the name of Rabbi Akiba Eger (Poland, 1761-1837).
Of course, the widespread custom in our community and in most Jewish communities today is to allow performing wedding ceremonies at night, and, in fact, most weddings are held at night. Indeed, the majority of Halachic authorities did not accept this ruling of the Re’em. The Sedeh Hemed (Rav Haim Hizkiyahu Medini, 1833-1905), for example, writes that it is permissible to perform Kiddushin at night, though he personally conducted the weddings of his children and students specifically during the day. The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in his work Rab Pe’alim (Eben Ha’ezer 1:6), writes that the practice in Baghdad was to conduct all wedding ceremonies at night, and no Rabbis ever objected. He thus rules that there is no need to perform weddings specifically by day, even on the level of "Midat Hasidut" (an added measure of piety). The Aruch Ha’shulhan (Rav Yechiel Michel Epstein of Nevarduk, 1829-1908) similarly writes that it is entirely permissible to perform weddings at night, and he notes that this was the widespread practice in Eastern Europe.
More recently, it is recorded in the work Yebakshu Mi’pihu that Rav Yosef Shalom Elyashiv (contemporary) permitted performing wedding ceremonies at nighttime, even in Jerusalem. There were those who claimed that the custom is Jerusalem is to disallow Kiddushin at nighttime, but Rav Elyashiv maintained that this is incorrect. He notes the work Eretz Haim by Rav Haim Set’hon that records all the established customs of Jerusalem, and no mention is made there of performing weddings specifically by day. Therefore, it is permissible to perform weddings both by day and by night, even in Jerusalem.
It should be noted that contemporary practice is to allow even giving a Get at nighttime, rather than waiting until the morning.
Summary: It is permissible to perform the Kiddushin ceremony either by day or by night.