I would say the ending scene of CH8 is the earliest where you get overtly romantic scenes, which includes physical touches (in varying degrees for each RO). CH9 is more plot-oriented, so CH10/11 is where you get more romance depending on your RO (CH11 especially diverges wildly depending on whose route you're on). R's route gets you the romantic scenes the quickest, followed by X, then A, while D is the slowest burn due to outside circumstances making it difficult for them and the Crown to have a relationship (so if you're into the forbidden romance trope then D is definitely the pick). CH11-14 include first kisses (and intimacy on X's route) for all the ROs (except for D lol, lots of almost-but-not-quite moments instead).
There's also a lot of emotional development happening for each romance route starting from CH7 though, the ending scene of that chapter forms the foundation for each of the romances and a major plot point for each ROs subplot!