How would they spend more time adding a homosixual couple rather than a heterosixual one?
If this was Oblivion, then instead of having Romana Faleria talk about how Tertius Favonius is a dreamboat, you would instead have Severius Atius talk lovely about Tertius.
I don't see how that would require any more time than having Tertius heterosixual.
Either way I don't mind. If they are int he game, then cool, if they are not, then cool
But to answer your question, when it comes to codding every second counts. It sometimes can take days to make code for even the simplest of things and any time spent on other stuff is time they could be spending working on that horse code and fixing bugs.
To make a gay couple would require that they make two new character models for each couple they added. Then you have to do voices overs for them, this is Skyrim everything Bethesda adds will have a voice over I promise you. Then you have to build their house, decorate it, place them into it, give them code, add scripts triggers and what not. All of that takes time.
I also want to add that when I say that, I am assuming that they have already populated the world so they would have to go back and add them in. But you know if they wanted to make a few people they added gay, then as long as they aren't going backwards then no, you are correct it really wouldn't take much time at all.