The mishna at the bottom of Ketubot 93b talks about paying ketubot when a man with several wives dies. (They're paid in order of marriage, which from context means order of kiddushin.) It then raises the case of marrying several women on the same day, and records that it was the practice in Jerusalem to add the hour and not just the date to the ketubah in that case (so a later court would be able to determine unambiguously the order of the wives).
From the Soncino translation:
[...] She also may not exact payment except on oath, if all [ketubahs] were issued on the same day then the woman [whose ketubah] preceded that of the other, even if only by one hour, gains [the first right]. And so it was the custom in Jerusalem to insert the hours [in such documents]. If all ketubahs were issued at the same hour and the estate is worth no more than a maneh [the women] receive equal shares.
If the mishna had just said that in that case we add the hours, then I would have assumed that this was a theoretical case. But it says it was the practice in Jerusalem. On 94b (h/t ray) the g'mara talks about writing the time in documents in general, but here the mishna seems to be specifically talking about doing so in ketubot.
Marrying more than one person on the same day seems unusual to me, but I am of course far removed from this time in our history. What circumstances would have led to this happening in mishnaic times?