by chapter 19, absolutely they have lol. I am a little bit on the fence about how long they would have waited, because I think it's equally likely that sunoo makes sunghoon wait and that he lasts two days before he decides he's already waited long enough lol. having said that, even if sunoo does make sunghoon wait, he definitely cracks during his preheat and decides he's waited long enough

so tl;dr they definitely get to business during sunoo's preheat, I just haven't decided if that would be their first time or not