I'm not referring to dinner and a movie or whatever presently constitutes a 'date'. I'm thinking of how best to avoid references to old technology or ideas if a writer is attempting to be current. Or the converse: how to capture the flavour and authenticity or a time that is still in recent memory of potential readers.
If a writer has set his tale in the Regency period of 17th Century England it is perfectly acceptable, correct even, to make statements like "A single man in possession of a large fortune must be in want of a wife." (Jane Austen, Pride and Prejudice). At the present time, no one would admit to being in want of a wife or husband or even a cold drink.
One of the challenges of writing a period piece, even as relatively recent as World War II, is getting the jargon correct, not to mention the behaviours and clothing. No mentions of the heroine wearing a racy push-up bra, when those dubious items weren't invented until 1947. That's where the internet is so handy for fact checking. It's like writing about a place you haven't lived in or even visited. Even with Google Street view and long conversations with those who have been inhabitants, inevitably a small detail will trip you up . . . and haunt you long after the book is published.
Attitudes change too, of course, but when was the tipping point? Sexual diversity, smoking, or even bringing reusable bags for grocery shopping have varied from unacceptable to acceptable to downright desirable or undesirable in public opinion.
I was recently reading a novel in which the protagonist couldn't get through on the telephone to another character, obviously because she was on the internet. I had to stop for a moment to consider how that made a difference. Down memory's path to the point where I recalled the screeching sound emitted if some unfortunate person picked up the telephone when the internet was being used. Ah, dial-up internet. Those difficult days were almost forgotten. By then my train of thought required me to check the date of publication.
Period costumes, manners and mores are far enough removed to be fascinating but portable telephones that look like shoeboxes are only laughable and in a dramatic crime series not the effect the director was going for.