The timer in Timed Practice should be stopped if you are trying to report a problem.
I was trying to report an alternate translation with an explanation during timed practice. The timer kept going and the session ended before I could complete my explanation. The timer should stop if the user is reporting a problem, then restart once the problem has been successfully reported.
If you use the chrome browser, you can add Duolingo Tweaks which does exactly this -- it stops the timer when doing timed practice. It adds a few other enhancements as well.
Go to the Wiki:
Then click "Duolingo Tweaks".
This discussion has been raised many times. And, I think the people who understand why it hasn't been implemented after so many requests, have explained it so many times that we generally just leave it be. But, it's been a while, so I'll give it a go. (Note that some people have explained it way better than I can and with far more reasons as to why pausing timed practice would make it a less effective learning tool.)
There is every other person in the course who makes it to that same spot who can report the same error either as they are going through the lesson or in Untimed Practice. So, it's not essential for you correct it. Duolingo's priority appears to be for us to get the most out of the Timed Practice feature as possible. To do so, we are required to be under unceasing pressure to respond quickly over and over again in the language we are learning.
However, Duolingo is not going to stop you from helping to improve the course. But, by prioritizing submitting that report from Timed Practice, you are making the choice not to prioritize your benefit from the Timed aspect of the feature, which is negated when you stop to submit a report. There is an Untimed Practice that people can choose that allows them to submit errors with no pressure from the clock.
I hope that helps explain why a pause button in the Timed Practice is not only unnecessary but defeats the purpose of having a Timed Practice feature. :)