Hi, one of the authors of the post, we will update the post with numbers from 256 GPU run within the next few days. We estimated the 256 run to be the fastest (13 days), but also the most expensive at $160k. The measured 128 GPU run would take 21 days but for $125k if you are interested in lower costs.
That is not necessarily a saving. If you have a let's say a team of five people each costing $1000 a day, those idle 6 days (not counting the weekend) would add up to $30k of wasted money. Then if you are working on something the competition is also working on, these lost days would add up and potentially cost losing the edge - could be quite expensive or even cost the business.