Thanks for your sympathy and understanding about German. 
As you’ve mentioned skills, I actually did learn to read to a decent level never managed to put together more than a bunch of words without a structure when I tried to communicate in German-speaking lands, by the way.
Just an extra comment about speed in SSiW, again based on my personal experience:
when I first tried challenges, I (obviously?) wasn’t able to say the whole sentence in those 3-4 seconds.
I’m not first language English and even have a very poor working/short term memory for words, so I couldn’t even remember what I was supposed to say let alone translating it into Welsh in so little time.
Having read the instructions and tried to follow them accurately, and failed.
I got really frustrated and had to choose between quitting the course, or “tweak” it a bit to my needs.
So I started using the pause button.
As little as possible, but as much as I needed to remember at least a few of the words and say them out loud.
This way, I managed to finish all Level 1 and 2. Rarely saying the longest sentences in full, but that’s where the tip that @Cetra reminded came handy.
And it worked, because I actually found out I had learned much more than I expected in fact.
Then with level 3 there was just no way for me to go further, even with the pause button.
So I read somewhere that in the Spanish course (not 100% sure but one of the other languages anyway) lessons come with a video where the sentence in English appears on the screen while it’s being said by the speaker. A bit like a subtitle, I guess.
So, I took my time and transcribed all the English sentences for all the lessons in Level 3, so that I could read them the same way instead of having to find them in my bad working memory while also thinking on how to turn them into their Welsh counterparts! And it worked, so I finished level 3 too.
This about the tricks I used once I walked out of the Germanitude, in case they may be helpful. 
As far as “why not giving more time in the first place, instead?”, a few more considerations:
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it was written somewhere, but I definitely can tell from my experience that a bit of pressure actually helps getting the brain alert and memorizing.
Of course if the pressure is too high, you get the opposite effect and brain shuts down. But that’s when pause button comes handy - and if one thing, I definitely think it would be worth writing more clearly that “no pause!” is the general rule, but there are circumstances when it may be advisable to do differently and each learner could/should find their own balance with it.
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I did each challenge only once, occasionally twice, no more. This because it the instructions were to avoid too much repetition. But also because there are things I can happily listen 10 million times (like songs - very useful by the way, to memorize sentences, if I may say).
But other repetitions get me bored and if it happens my mind just wanders away and there’s no way for me to focus(for example with Duolingo at first I thought I had to go all the way till level 5 on each lesson and I just couldn’t stand it)
A few months after I finished the Level, I went back and tried a few earlier lessons. And to my surprise, believe it or not, the time I had to say the Welsh sentence most of the time was…too long!
And in the end, got quite a good grasp of the structure and rules - even though not in a gradual and slow way, more like children-like way of learning.
To my understanding one of the aims of having a short(er) time is to help you reach faster into “automatic gear” as opposed to overthinking and/or trying to translate word by word.
I found videos by Anthony Lauder very interesting and useful, especially this (I’m almost sure it was this video, but you can have a look at his channel): https://youtu.be/Ntr-l8Rng7E
The idea is similar, I think, to what another technique called “Extensive reading”. Have you have heard of it?
If not, it might be interesting for you since you seem to be more into figuring out the language structure and system and understanding rather than reaching some degree of spoken fluency in everyday life, or chats and social events that you’re unlikely to get involved in. Did I understand right?
In any case for you or anyone else interested, there’s quite a few videos about the theory, but when I moved to trying to acquire some reading skills it seemed very efficient and rewarding to me.
(BTW I started with Colin Jones, and then the Amdani series and Lois Arnold to name a few).
Ok, just a few more notes if anything helps!
But I think its accepted that it doesn’t suit everyone… 
