The other prompt for break-time is when it hits me that what I have achieved so far in the current draft is the dawning realization that this is not working, and a new draft must be started from page one.
At that point I tend to put on loud music and sing along even louder; make a fresh pot of tea, and sometimes banana muffins or, if I am really tossing more than 25 pages, something stronger. Like cookies. Or a glass of Bourbon. Maybe Janis Joplin.
The other way I know it's time to take a break is if it is time to pick up a kid from someplace.
In that circumstance I generally skip the making of the tea, etc., but not necessarily the singing. Which sometimes scares the neighbors in the elevator, but it's New York. I will not be the weirdest person they encounter that day.
I tend to WANT to take a break when it hits me that I have no earthly idea what to write next, but since that is an experience I have multiple times per minute, at least during the first maybe 20 drafts of a book, I try very hard to resist it.
Some days I think I would be very good at sluggery, and must rage against the temptation toward it.
When do you take a break? What do you do for it?