Step 5: start distilling
Heat the pot up until the water starts boiling. Did I mention that you might want to do this outside? The catnip vapors don't smell bad, in fact it's a pleasant minty smell, but it's pretty strong and is likely to linger for a while. At least open up all the doors and windows.
Once the steam starts to condense on the lid, cover it with some of the ice. This will help condense the vapors more efficiently. To put some hard numbers on it, my distiller was able to condense ~10 mL in 15 min when I had the lid just cooled by air. But with ice on top, it condensed ~100 mL in 15 min.
The ice will melt as the steam condenses, hopefully collecting in the glass in the center of the pot. This is good.