Warning- this is fairly convoluted stuff, so you might want to refresh your memory on Elizabeth’s visit to Hunsford before you dig in. Also, as a caveat, I have not looked into every permutation of fixed dates and flexible dates as they might lay down in every year between 1797, when she started First Impressions, and, say, 1816, three years after P&P was published. This may have been laziness on my part, but as one of the voices in an earlier discussion noted, "It's fiction!" So long as my dates laid down pretty tightly with Austen's, I was satisfied.

Most efforts that I have seen to place P&P in time support 1811 as the most probable start date for the events in the novel; these arguments, however, revolve mostly around the historical events of JA’s time, when she wrote and published her novels, and conclusions and inferences driven by a good deal of research into matters outside the novel—and very little of this information comes from JA herself. I feel better just taking the author’s own words in the novel itself. In considering the specific years in which P&P takes place, we have to begin with the two hard dates in November given in the novel: Monday the 18th (Mr. Collin’s arrival at Longbourn) and Mr. Bingley’s ball on Tuesday, the 26th. It is accepting these hard dates that forces us to 1799 and 1811: those years have the proper dates in November. While most arguments have focused on either 1799, as being the closest to the writing of First Impressions, or 1811, as being the closest to the publication of the P&P novel, it should be noted that 1805 and 1816 might also be considered; but as they lay down very much like 1799 and we have no real reason to invoke them, I will leave them out of the discussion.

It is the visit to Rosings and the dates Easter falls on that, in my estimation, points to 1799 as the appropriate start.

“March was to take Elizabeth to Hunsford…”

This doesn’t give us much by itself, but when we add the other limitations to the visit found throughout the rest of the novel, we get a more concrete timeline. First, we have the end of their journey coming within the first fourteen days of May:

“It was the second week in May in which the three young ladies set out together from Gracechurch-street…”

This gives a feeling for the end date, but it’s still vague. To place Elizabeth’s visit more precisely, we have two pieces of evidence that she was there for 6 weeks: On the morning she gets Darcy’s letter, the text refers to “The five weeks which she had now passed in Kent…” As we will see below, this was just over a week before she was to leave herself.

On the Saturday of the cousins’ departure, Elizabeth tells Lady C. “I must be in town next Saturday”. Lady C. responds “…you will have been here only six weeks. I expected you to stay two months. Mrs. Bennet could certainly spare you for another fortnight…”

But which six weeks are they? We have to link several points together to reach a conclusion. On the day of Darcy’s proposal, Colonel Fitzwilliam assures her that they are to leave the coming Saturday:

“Do you certainly leave Kent on Saturday?” said she. “Yes—if Darcy does not put it off again…

Darcy proposes, Elizabeth gets his letter the next morning, and the cousins leave on the day following (“The two gentlemen left Rosings the next morning…”, which by the Colonel’s account would be a Saturday. Therefore, Darcy proposes on a Thursday, delivers the letter Friday, and leaves on Saturday. So far, so good. Now there are several references that tie to this particular Saturday:

“The five weeks which she had now passed in Kent…” (this on her morning walk the day prior, when Darcy gives her the letter).

And, one we have used before, Lady C. speaking of Elizabeth’s departure the following Saturday: “…you will have been here only six weeks. I expected you to stay two months. Mrs. Bennet could certainly spare you for another fortnight…”

Finally,

“…And if you will stay another month complete, it will be in my power to take one of you as far as London, for I am going there early in June.”

These last two quotes are from the day of the gentlemen’s departure, making the following Saturday (the one Elizabeth and Lady C. are discussing) either the very end of April or the very beginning of May, as “another month complete” will take them to June. The context of that conversation suggests the Lady C. really meant four weeks, which would definitely make their departure the beginning of May, but the point is debatable.

But now we must consider Easter. First, we must remember that the cousins’ stay lasted less than three weeks. As Elizabeth tells Wickham later in the novel:

Wickham: “How long did you say that he was at Rosings?” Elizabeth: “Nearly three weeks.”

Also, the gentlemen arrive the week before Easter:

“Easter-day, almost a week after the gentlemen’s arrival…”

So, given the cousins’ departure a week or so before the end of April / beginning of May and the fact that they were there three weeks, Easter needs to be somewhere around the second week of April. Now we finally have a test of our possibilities. For the years in question, the dates for Easter were:

1800 13 April
1812 29 March

So, if it was 1812, Darcy would have left on April 11th (the second Saturday after Easter that year) and Elizabeth on the 18th, leaving more than six weeks to June, not four. In 1800, Darcy would have left on April 26th and Elizabeth on May 3rd, leaving the full month of May until Lady C.’s departure for London “early in June”, as required. This is the only way you can make all these facts—Elizabeth’s six-week stay, Darcy’s three-week stay, Darcy’s arrival a week before Easter, and Elizabeth’s leaving a month before June—all work together.

The dates of the novel for the rest of the year, including the Northern Tour and Lambton, Lydia and Wickham’s marriage, etc., vary only by one day between 1800 and 1812, and the only hard date we can look to, a letter from Mr. Gardiner dated Monday, 2 August, does not occur in either year (in fact, it occurred only in 1802 and 1819, neither of which can support the rest of the dates), so we can’t support either year from those dates. Anyway, there it is; I hope you like it, and, more especially, I hope that it was comprehensible.