Generally speaking, I don’t do any writing after five PM. That’s a rule mostly for my own sanity. I don’t want to spend every hour feeling like I really ought to be writing. And, let’s face it, writing is not a very time-consuming activity. The number of writers who do more than two hours a day at the keyboard is shockingly small, and even those two hours can sometimes be too much. If I have no idea what I’m doing, it’s better to do no writing rather than spend two hours banging on the keyboard without producing anything worthwhile.
But every day I do face the task of determining a proper stopping point. This is actually a somewhat rarefied problem, since most of the time I’m blocked and unable to write. So there’s a natural tendency, on good writing days, to keep on typing. After all, when the inspiration is really flowing, I can write two thousand words in under two hours. If I kept going at that rate, entire novels could be written in ten days (this is something I once did, although the novel didn’t sell).
Still, after two thousand words I usually think it’s better to knock off for the day (on fiction writing that is. Paid freelance work is something different). I can’t quite explain the thinking here. At the time it always feels like laziness, but I usually find that a day or two of thinking about the book makes me realize that my intended direction wasn’t quite right. Oftentimes a pause gives me the time to consider the draft and save myself from trouble.