There is a bracha (blessing) made after the first time a Chosson and Kallah have relations in the case that she was a basuleh (when there was a complete bia.) The makor for this Bracha is the Rosh (Kasubos Perek 1 Siman 15 -- makor in the Gaonim) and is brought by many other rishonim as well (some don't bring it.) However it's brought in Shulchan Arun Evan HaEzer Siman 63 Sif 1. However l'maseh it is my impression that those that say the bracha do so without Shem U'Malkus. If someone didn't recite this bracha by the first bia (or right afterwards) may it be said even after? The question is perhaps not so strong since there is no Shem U'Malchus. However in general is there a reason or an inyun to say it even after the first time if it wasn't said to begin with (not necessarily by the second time the couple has relations, perhaps even at a general time when the person remembers that they didn't say the bracha.)
See the Chelkat Mechokek to the Shulchan Aruch there who rules that the only reason it isn't recited Over Laasiyatan (before the action, as is generally required with mitzva brachot) is because there is no way to know before hand if the woman is actually a Betulah.
There is a general argument if the requirement of Over Laasiyatan in general is absolute, or if the blessing can still be said after the mitzva post facto. The Rama (YD 19:1) rules like the Or Zarua that post facto the blessing can still be said after the mitzva, but he qualifies that it must still be סמוך = adjacent to the mitzva. Accordingly, it would seem that the allowed time for your bracha is only 'adjacent' to the original time (I don't have an exact number of minutes on that).