There have been times that I've posted before finishing the article. Mostly on longer articles where I know I'll forget what I wanted to say by the time I finish. In those cases, I do search the article and comments to see if my thought was addressed or made by somebody else. It's not perfect, but I think I've only looked stupid once*, because a poster made the same comment, but didn't quote the article text.
I think the timer would annoy me. I'm generally considered a fast reader. I don't speed read, but pretty much the only people that read faster than I do are speed readers. If they implemented a timer, I'm sure I'd be pulling up the console within a week.
* For this reason; I look stupid plenty often for other reasons.