Yesterday's etch on the left - 50 minutes, today's etch on the right - 1 hr 20 minutes. You can see the difference. Shame all this wonderful experimenting is not exact; as the time taken varies depending on the age of your solution and the amount of silver that has already been etched in it.
Might try a bit of upside down etching tomorrow, as I now understand the feather thing is good for nitric acid, where it releases bubbles when etching, but the silver etched in ferric nitrate needs to be suspended upside down so residue can drop down.
Why hasn't anyone written a decent book on this?... Now there's an idea.