Step 3: Add PCB and you're Etching.
If this is the first time you're using this batch of solution (and I presume it is), it'll etch super-fast. This small board took only 2 minutes. Yikes!
Since I use a deep container, I tend to swirl it around as it etches. This stuff is so active, though, that I'm not sure it's necessary.
Keep the window open for ventilation because the starter solution gives off a little chlorine gas. (The end-etchant gives off much, much less.)
Also, note how the etchant gets greener over time as it eats away the copper. This is good news.
What's happening is that you're dissolving the copper from the board and turning it into cupric chloride. In the long-run, the cupric chloride will be doing most of the etching (instead of requiring disposal). For now, just watch your solution turn light green. Next time you use it, the color will deepen.