I don’t think there is a particular click, but initially, you are really focusing on every single improvement you make, then you stop worrying about it, you focus more on the process. Then suddenly you get flashback of your old you that was not able to understand something specific. Thus you get a “click feeling”.
For example, I started doing a lot of article translation to get used of the “reversed order” of how Japanese sentence are written. Step by step, it was easier and easier, but I stopped really worrying too much about the time, I was just more focusing on reading. Then suddenly one day I thought “I will read this article quickly”, looking at the clock because I was waiting for my meat to be cooked, and I realized that I read the full article in less than 5 min when in the past it would take me 45-60min to do one …
So I felt a “click”, but the click was just me not really focusing on the improvement for a period of time and then suddenly realize what I achieved