...after Catherine had met Isabella. So James would have known Isabella for about two weeks total (unless he had snuck visits between Christmas and Bath that no one speaks of). Given what we know about Isabella's nature and prospects to make James a good wife, can we wonder that he has made such a bad decision in asking her on such short acquaintance.

But of course Catherine has pretty much fallen for Henry in even less time and would likely say "yes" if asked to marry him. So who knows? How long did Jane know Bingley in P&P before everyone expected a proposal? How long did Emma know Frank Churchill before friends expected a proposal or Frank know Jane Fairfax before it actually happened? How long did Elinor know Edward before Fanny feared it, or Marianne know Willoughby before everyone assumed it? It does appear that such expectations did not take particularly long to grow. Not every proposal seemed to take very long, even the good ones JA tells us about. Fanny Price and Edmund Bertram, and Emma and Knightley seem to be the rare long-time acquaintances who eventually tie the knot.