So in native turkish speakers' speech, i noticed there are very common little pauses at some points in the sentences. I don't understand enough to get where exactly, but i feel like it must be to clarify the meaning of the sentence, or at least to avoid confusion. In this particular sentence the TTS makes things sound like "ne zaman" is one very strong unit, with a tiny pause before and after and no room at all between the two words. Would that be overreading the tts or would you say that's how a native speaker would (should?) pace this sentence?
In other words, would "Yolculuk, ne, zaman, başladı?" sound really off compared to "Yolculuk, ne zaman, başladı?"
Native speaker here. It is my observation that the pronunciation of TTS generated voice is of quite low quality in this course. In this sentence, however, it is surprisingly quite good. Your description about this particular instance is quite on target. I can say in this particular example the TTS speaks as close as possible to how a native speaker would speak.
About your observation on Turkish speakers' speech: I can't say that I am aware of it but I have the impression that maybe it is about last and first letters of adjacent words. Take "ne zaman": The first word ends with a vowel and the next word start with consonant, rendering that part extremely easy to utter in a fluent way. Like you said, the two words sound as if they are one single word, like "nezaman". This is normal and people speak that way. But take "yolculuk ne" part. That's a bit more difficult due to 2 consonants come one after another. No matter how you try to pronounce it as "yolculukne" it would be less fluid, and you have to display a bit more effort to make it sound as if they are one word. So I believe those pauses you mentioned perhaps audible to you naturally at some word boundaries. As such, I don't want to say awkward but "Yolculuk, ne, zaman, başladı?" may indeed sound a bit unusual if it is delivered by a native speaker.
I would also add that "ne zaman" is no longer understood as "ne" + "zaman". Note by the way that this is hardly grammatical. We would never use "ne" with a noun. Except for certain question words: ne çeşit, ne vakit, ne cins, and so on.
I'd say "ne zaman" is one word that's spelt with a space.