To be honest, I was certain they hadn't done it, if only because the implications of Tsukasa's regeneration sounded like it would be unpleasant for either or both of them... but after it was clarified she could at least delay the regeneration effect, I started to accept the possibility. Especially with how friendly they've gotten by the 300-ish chapters.
However, it is also important to remember they're still only a couple of months into a marriage where they barely really knew each other beforehand. It's maybe around 5 months, to be speciific. Story essentially started in May, with Nasa's 18th birthday. We shifted forward to June sometime in the 60s of chapters, then for whatever reason skipped forward fairly quickly to July not too long after by Ch.77. We don't see mention of time moving forward into August until Ch.159, and the only implication that we have advanced into September happened in Ch.228 with a conversation between Tsukasa and Aya over whether it's still summer anymore, with Aya making an absurd comment about September being the start of her personal summer.
Far as I'm aware, the trip this extra takes place during is within 5 months of the proper start of their relationship and marriage, simultaneously, and as of around Ch.330, I still hadn't seen mention of time definitively advancing to October.
As context, the flash-forward chapter around 140-ish gave the impression the story will be coming to a conclusion some time in December of the year the main part of the story takes place during (I interpret the present-day part of the story as taking place entirely within the year of 2018, the year ToniKawa started publication- keeps it simple, that way).
This means that if the story continues to extend in chapter length, the longer the months will take to pass, since, as far as I'm concerned, if the story reaches December, we're probably in the end-game. As it stands, we still have all of October and November in-story before that happens.