Thanks for the chapter, MS.
It's funny, sure, but he's got a point. Apparently by the author's pen, Jirou's getting real high off the idea of romance, such that he's betting Akari on whether or not he can pass an entrance exam; Akari seems to be in on it, too.
Whether or not. Did either one of them think about what would happen if either of them either fail or is otherwise unable to attend his/her school of choice? This is the kind of thing people do when they're in love with the idea of being in love, rather than actually just being in love; for some people, their love of the idea is all they have.
That's the actual "wanking"--Jirou's waxing dramatic over a prize he's already won.
If they love each other--which they do--there's no reason to wait. There doesn't
have to be some proper time to start a relationship for maximum romance points or some other similarly stupid abstraction; they should declare it immediately to themselves and the world immediately, because they don't know what tomorrow brings. If all it takes is one bad emotion to cast a pall of doubt on the entirety of their loving connection, then they don't have the time to waste, because every day has 9001 sources of such an emotion--especially for people who are highly emotional.
That said, they're already in a relationship anyway. If either of the two started gallivanting with someone of the opposite sex, there'd be hell to pay. It's not because they're "just friends, but it's complicated".