Er, he makes a glottal stop because he finds it an easy, safe, and pleasant experience? Sorry -- I didn't mean to prescribe a pause, as opposed to a glottal stop.
You're supposed to have a little pause there, not a long vowel. You can get that with a glottal stop, if that's easy for you, and you can also get it with a tiny pause.
I think that the reason you asked that is because Duolingo do not teach Esperanto "the right way" in my opinion. They don't explain enough about the language and how it works and put the exercises as the main thing and let you understand most of the language by yourself. One might not understand all the word combining, for example, and memorize words that he doesn't really need to memorize. For starting to learn the language, I think that a site as "Lernu!" is much better, although Duolingo is a great exercise, once you've got the idea of the language.
Personally, I like Duo's method, which is having to figure things out myself. Figuring things out myself makes me think, and it's the thinking about it that keeps me interested. The spoon-feed method bores me to death. I don't even look at the "notes and tips" and I don't "hover" over words. I just take a guess. I'll probably go through the tree twice, and I'll look at things in more detail the second time around. I think if I try to understand everything as I go along, I'll just get so bogged down with information overload that I'll just give up.