... remember what Linden said in her "Courtship rituals" post - that people of JA's time were supposed to do their courting without anyone else knowing about it. If Darcy had gone running off to the Parsonage after finding out whether Elizabeth was alone there (except for the servants), it would have been too obvious for words to everyone there, even if he claimed that he just wanted to know whether there was any little thing she needed. I think that he was probably following the approved "Emily Post" method of his time when he sneaked away from Rosings (with nobody the wiser) to make his proposal, and even had a convenient (if not very strong) excuse for his visit when he first arrived. (You might say that earlier in the book, Mr. Collins was nowhere near so subtle when making his declaration, but when was Mr. Collins ever subtle?)