There were two economic factors affecting the length of enagements in those days. The first was the time it took to arrange all the marriage setlements between the lawyers on both sides. This commonly took about two months, in cases where there were fortunes to be secured, but it didn't have to take so long. In Lizzy and Darcy's case, for example, he seems to have proposed about October 16th, according to Ellen Moody's calendar, and of course, as JA tells us, they were married at Christmas. Obviously, in this case, the legal haggling didn't go on very long! However, if a couple got engaged before they had any money to marry with,engagements coudl literally go on for years. Cassandra Austen was in ths situation- her marrriage to Tom Fowle was put off until he came back form teh west indies, presumably expecting some financila remuneration for this trip. Many, many, impecunious people waited years before they were married. One of my favourite examples of this is of Edward Jenner, the smallpox pioneer, who was engaged for five years whilst he collecte d together enough money to marry and set up a house, and then spent the next ten paying his wife's medical bills.

If there were no fortunes to consider (because there was no fortune!), a couple stil had to wait three weeks for the Banns publication of their intended marriage to take place in their local church. If there were no real impediments and a couple didn't want to wait for Banns, they could pay for a special licence, which allowed them to marry as soon as they coule "light upon a bishop" who would issue the licence. Or they coudl elope to Gretna Green, and get it al over with in matter of days, as Lydia intends to do.

From that,I don't see any particular "tendency" to either long or short engagements.