Unfortunately, if I tried to graph my writing progress by the quarter-hour, it would probably disrupt the process too much; it's only when the words aren't coming easily that I hit the wordcount button every sentence to see if I've met quota yet. I suspect, though, that it would be an interestingly shaped curve. I know that I achieved 741 words (net of revisions) tonight, in just about two hours, but the first 100 took the first half hour. On weekends and holidays, I sometimes hit the point, somewhere beyond 700-ish, where I can get the next 500 or 1000 without even noticing, though I do tend to lose track of time too at that stage.
One long-ago summer night, I wrote 7000 words in a sitting, but that kept me up until 3am. On a work night. (Fortunately, my boss was one of the people cheering me on and eagerly reading the chapters as soon as they were finished.)
Ambassador is now at 22,079 words, and I'm almost out of gaps to fill in the first half. There's still the scene in the Honolulu airport that needs a rat added, and one scene of saucer-on-submarine action, and then there's nothing but grand finale and wrap-up, so maybe it really will be done inside 30K.