Script: AO3 reading time estimate

After a certain friend of mine remarked that she'd been up until 3AM reading fic three nights in a row (a "fictim", as Tumblr would have it), I remarked that it should be pretty straightforward to write a script that will estimate how long it will take to read a fic and pop up a warning when it thinks you'll finish too late for comfort.

So there's now a bookmarklet that will calculate how long it will take you to read a fic, and also a userscript that will do the same and then warn you if it think you'll finish after 1AM (or however you configure it).

These are both still in very early beta, so please let me know if you encounter any weirdness or have suggestions.
http://random.fangirling.net/fun/ao3/work_reading_est.html

( I don't know if a point-by-point retrospective on developing this would be of any interest to anybody, so it's behind a cut. )