I have always ask to myself at this part of the book how is posible that Mr.Darcy went to Hunsford to propose to Lizzy when everybody was at Rosings and nobody seems to care about it. My first guess is that he went after dinner when men and women split before the tea. In this way at least her aunt can't ask him any impertinent question. But this leaves Coronel Fizwilliam and Mr.Collins knowing he has gone. I assume Coronel Fizwilliam posibly knew what he was about, but it's not very odd that he leaves the dinner? or it's not?, maybe it was not expected for him to join every gathering his aunt arranges? But we know that he has been with them at lesat part of the evening because he knows Lizzy is unwell.