..and personally, I htink that she used a calendar, but deliberately fudged a few dates in order thatanyone who really wanted toset it at a particular time would have a dickens of a job in doing so! She does exactly this with her distances and places- giving just enough information to make it realistic, but, if you look closely it's absolutely impossible to pin down Rosings, or Pemberley, or even Meryton to an exact location.Just try drawing a map of Meryton with Netherfield and Longborn on it, and the distances /directions she gives, and see whati mean. The same with Highbury and London, Kingston and Box Hill- one has to bend England to make the measurements fit.

As regards to time, and P&P, the (real) militia movements of 1794/95, and what we know of Austen's contact with the militia regiments fits best, which doesn't align with any other ssuggested timeline whatsoever. Personally, I think JA intended it to be fuzzy...either to protect real names and real epople, or just because she enjoyed making puzzles.