Not enough time
It used to be that I would finish a lesson with about a minute or more left in my allotted time. Now, I fight to have 20 seconds remaining. Duolingo decided to give fewer seconds to each right answer, and now I'm fighting it. This, in turn, makes me hurry and makes me less careful. Does giving me less time to do a translation make me learn better? I don't think so. It just gives me more incorrect answers. Why did you do this, Duolingo? Give us our old time rewards back, as well as our monthly totals. Just having the daily and yearly ones aren't enough.
I just got switched over to the new version of the website. (I have my likes and dislikes, but those are irrelevant right now.) I am not sure that the reward time is less, but I do agree that there is definitely less time. Also, the animation between problems is faster, and makes you feel more rushed. I am not sure what is making the time run out sooner, but I definitely feel there is less time. I have almost the exact same problem as stefanschets, although it is not as exatterated since I am notorious for having 100+ WPM.
Timed Practice is an item you can buy from the Lingot Store. It is designed to prepare you for the stressful environment of having to reply to a native speaker right where you are without pulling up Google translate.
In the old version of the website, you start with 30 seconds that are continually draining. Seconds get added to the clock every time you get a problem right. If the clock reaches 0 seconds then the practice session ends.