When there’s something big and ugly between the teeth of your interlocutor, you’ll likely say that immediately or not.
It’s nearly impossible to say something about it, 45 minutes in the conversation. You just socially ‘can’t say it’ anymore after some time… The window closed.
The same goes for things in relationships that are established already for some time. The shared relationship-culture accepted that ‘it’ is like this. Whether it’s about farting, shaking hands, not speaking your opinion, paying too late for invoices.
Changing it is hard, socially nearly impossible. You never complained about it before. Why didn’t you say that earlier?
If you notice something, rather do something about it immediately, before it becomes too big to handle.