(It would be useful if Charlie and Billy could really work on my books when I'm not there! Or perhaps not — depending on what they came up with.)
I follow a timeline in my more recent novels. I didn't in my first books, the traditional Regencies, which I think it the usual thing in most Regency romances. Some of Georgette Heyer's are fixed against events in the war, but most could be in any year.
My Company of Rogues books were pinned to time from the beginning, however, because the plot links to the time around Napoleon's abdication in 1814. Having begun, I had to continue because the seasons and pregnancies clearly mark the passage of time. I've written 16 books set between 1814 and 1817, and the time between them is often very small, but I'm pushed onward. And here I am in 1817, with peacetime bringing economic depression, unemployment, and a high cost of living.
And social unrest.
I didn't intend to become embroiled, until a man slipped into a lady's bedroom in an inn, clearly avoiding people pursuing him with unpleasant intentions.