Practice against time has an annoying problem
Clock is ticking out also when duolingo "checks" the answer, so sometimes the whole freaking clock runs out at the first question already! That's very frustrating and annoying. I cannot proceed more than 2 or 3 questions, and time is wasted on this "checking". That's not fair at all! Devs please if you don't mind to code the check button to pause the clock when pressed during checking the correct answer until next question is up? That would be relieving and highly aprreciated! Thanks a bunch!
I have experienced this, too, but I don't think the problem is so easy to solve. The actual check (lookup for the answer on the server-side) doesn't take much time at all, it's close to instant.
It's the time your computer needs to connect to the server that is spent while you're waiting for response, not the look-up.
This means, even if they pause the clock while checking the answer, it would already be too late because of the time needed to send your answer to the server (which takes place before the watch can be stopped).
Disclaimer: I can't say for sure how their system works, but I believe this is not far from the truth.