] I've got a huge book on Reynolds, and I was reading his biography yesterday, so I know when he died. In fact, he was completely blind by 1791, so if Austen actually had Reynolds in mind as the painter, P&P would have to be set in 1790 at the latest.
We have a larger margin, since all the portraits seem to have been done 5 years before the main action of P&P takes place.
There are two portraits of Darcy. One the miniature of which Mrs. Reynolds says:
"And that... is my master—and very like him. It was drawn at the same time as the other [Wickham's]—about eight years ago."
And the large one in the gallery:
" 'in the gallery up stairs you will see a finer, larger picture of him'... Mrs. Reynolds informed them that it had been taken in his father's life time.
And from Darcy himself, we know that:
"My excellent father died about five years ago".
Georgiana's portrait is not recent (a mistake from P&P2) since it's a portrait when she was a child:
"Mrs. Reynolds then directed their attention to one of Miss Darcy, drawn when she was only eight years old."
Since she is sixteen:
"Miss Darcy was tall, and on a larger scale than Elizabeth; and, though little more than sixteen"
Then her portrait, as Darcy's and Wickham's miniatures, was taken 8 years ago.