got mine on 60 farming the first room in Cragmore. I am guessing that the 20 in 20 mins is a timer for gems. Once you get over 20 in less than 20 mins there is only 1 trash item in drop. So there are only spots for 2 items in and you need to free one up to get rod to drop. It was taking ~12 mins to get 20 nodes so took me a bit over half an hour.
I got my broken metal rod today from skill node in Phantasmal Fortress. It is a low drop rate apparently, but it was the 3rd item in the box so there goes that theory.
Comments
--┐ - broken
--┬-- balanced
--^-- dented
≈≈≈≈ battle worn
≡≡≡≡ infused