If you were not logged in, then the conversation happens on the Kindle itself so yeah it's gonna be slow.
If you were logged in and the "backend mode" was enabled, then the delay will most likely be fetching the article images, compressing them and converting them to jpeg on the backend, but there's a setting to choose if you want to embed images or not.
I know what the delay was for, I mentioned it in my original reply. My point is, there's no visual indicator of what's happening. You click the button, and you don't know if the button's been clicked. The person wonders, "Did I miss?" So I, as anyone would, clicked again after a moment. And again. Still no indication.
I then moved on, looked at other options, clicked the epub, downloaded that, then the mobi option popped up.
Again, it looks neat. I'm just saying "put some feedback to indicate the button press worked", especially if it's an op which can take some time. It's standard UI stuff.
Good luck BTW, seems like a nice project.
Thanks for the feedback and the compliment!