At this point when in 0.4 both MC and aunt already did some "real kiss" then the chance they goes for more physical or intimate action will very likely. I don't think sex will come soon, with how Amellia personality is potrayed in game, she is not a woman who just jump on a guy because of the husband forget the marriage anniversary, she sad of course but not that broken, unless stupid husband cheating on her and she caught or have evidence, or something extreme similar, not only that but also the "gap" between her and MC, she is not entirely stupid, she aware of MC affection atleast to some extent, thus she hesitate of stepping beyond the bound (MC is her nephew after all, blood related or not). So i predict sex will come from 0.8.
Also depend on who get focus on each version, if dev just focus on the main couple then it will be very soon, but next version look like it focus more on the eldest daughter