I’m not entirely sure what the problem is, unfortunately. Sometimes if you have a bad internet connection it can be very slow to load, but you should always be able to click it. Are you talking about during the review right after you learn a lesson, or the next review after that?
As for waiting an hour, unfortunately that’s just how WaniKani works. They have lots of good reasons for it, and you can read more in some other threads. Like these: