What is the urgency of a husband and wife resuming relations after the niddah period? Where is the line drawn between conflicts that warrant pushing off relations, and those that do not warrant it? Some might be fatigue, illness, business activities that might or might not jeopardize one's livelihood, other schedule conflicts (performing arts rehearsals, chavrusos).
As Seth commented, Consulting Your Local Orthodox Rabbi is always an appropriate first step because your particular facts could result in a totally different answer than the generalized citations to authorities that are offered here.
As I have reviewed the sources, the rules of appropriate sexual behavior are not very well defined for every situation, and some proscriptions in the Talmud and the Codes are viewed as binding by some and as advice by others. Again, a reason to CYLOR. Rambam, in the Mishna Torah, Chapters 14 and 15 of Ishus, goes into some detail about the obligations of husband and wife to have relations with their spouse. I believe that these sources assume that both husband and wife are healthy and each have a healthy interest in sex. Accordingly, these would suggest that the couple does all that is possible to get to the mikvah at the appointed time and have relations that night. But there is no obligation to have relations that night, and there is even concern that the pressure on either partner will result in a loss of shalom bayis. On that point, I think that Rabbi Frand's tape on Shalom Bayis is helpful.
Poor health, fatigue, business conflicts, even Daf Yomi classes, are common conflicts with shalom bayis in the bedroom. Nevertheless, the Halacha recognizes that both husband and wife have conjugal obligations to make time for intimacy, Mishna Torah, Ishus 14:7-8; Shulchan Aruch Orach Chayim 240:1, and most authorities will urge the couple to make allowances. If the wife is too fatigued when the husband comes home regularly from work or Daf classes, they will encourage him to make changes in his schedule. If the wife is fatigued, for example from mikvah night preparations, she might be encouraged to take a nap in the afternoon, and the husband will be encouraged to do what he can to facilitate that (like taking the kids out for an outing without Mom). Compromise, consideration and compassion will go far.
There will be no cut-and-dry answer on this one.
I have heard Rabbi Barry Freundel say publicly that he tells young men before their weddings: "mikvah night, you have the responsibility to make the night special for her." He mentioned a fellow who decided to forgo an important business dinner so he could be home with his wife, even though that meant missing a promotion. (My impression was this was meritorious, not obligatory.) Of course, if the couple is stressed because of a tight financial situation and that promotion would honestly help ... again, every situation is different.
Yoatzot.org has reprinted several questions from women who are too anxious on mikvah night; if it really, really works better for the couple to wait, then that's probably the right thing to do.
Once again, ask your rabbi. And your rabbi will ask how your spouse feels, so make sure you know that too.