Timers are a love'em, hate'em feature for me. If I knew my material, I'm sure they wouldn't bother me at all. They might even be fun, adding a bit of a gaming aspect to the quizzes. However, if I was struggling, having the added pressure of a timer would probably my teeth on edge. Cue panic attack (not really, but you get the idea).
Therefore, while I love the idea of timers, especially for folks who [u]really[/u] like them, I'm hoping they'll be optional. If you (as in you, マイコー) have the ability to customise them such that they show up on an as-needed, as-wanted basis (quiz-by-quiz, question-by-question or style-by-style), that would be ideal! I'd definitely turn them on when I'm confident and keep them off when I'm not. Perhaps they could be introduced by level, so level 1-4 terms are untimed but higher levels get more and faster timers? My rationale is, by the time a term hits level 5, one should be fairly confident with it.
Here is another question, piggybacking on this topic: Would they be count-up timers (the faster you answer [correctly, of course], the more points you earn) or count-down timers (you have x-seconds to answer)?
Summing up: great idea, I'm looking forward to hearing more about it!