A meaning appears and you say it out loud before the timer runs out. It shows on the spot whether the words you "know" actually come out.
Why put a timer on it?
Conversation gives you no thinking time. Without the clock, every word you can reach eventually counts as known — and that gap is exactly why words do not come out when you need them.
What happens if I miss the time?
It moves on, and the word you missed comes back around. Your time goes to the words you cannot yet produce.