Semi-complex idea, more easily seen than explained, but here we go.
I was re-reading Harry Potter and the Sorcerer's Stone recently to get a feel for the way J.K. Rowling passes an entire year in a fairly short book that feels content packed, and I noticed something very common which I hadn't previously put any thought to.
With respect to the passage of time, the book's voice changes drastically here and there. For many pages it follows the minute-to-minute actions of the character, e.g. "Harry walked to the bathroom and donned an owl costume. Thus clad, he ran out among the crowds of Rockefeller Plaza and began to scream at random, throwing his arms in the air and leaping wildly."
But at other times the voice zooms out and passes hours in a sentence:
"Hermione didn't turn up for the next class and wasn't seen all afternoon."
Maybe this seems simple, or obvious, but I think it's a tiny piece of brilliance, and something that all good writers can do and frequently do do but which does not necessarily come easily to new writers and which maybe many people don't think about.
I see this happen with days, weeks, months, even years. And it isn't trivial to just drop it in there. In fact I've found it's very easy to interrupt the flow of your writing by shifting the rate of time passage in anything less than the smoothest manner.
So the question is: how to cleanly change time scale and avoid making a somewhat jarring break in temporal continuity? How to go from following a character second-to-second to briefly relating what the character did over the afternoon, the summer, the rest of his forties? Tips/Exercises for practice are always good, if anyone knows any clever ones.