Has this changed recently? I know when the program started, I had to do the full 40 rentals. I had 120-ish paid rental days. And I know there have been threads here from folks who generate a ton of revenue (say, $4k-5k over 150-200 days) and are only Five Star.

Everything I've seen says you need 40 rentals or $7k revenue. In fairness, it seems that it should be days or simply dollars, as the idea of a "rental" isn't a meaningful unit of measure. But I hadn't heard that Hertz had tweaked the program to make this so.