I trained under Dellinger briefly. 30/30s were a staple for the middle distance guys. 30/40s were more typically for the distance guys, with the 40 being running a 200, so it totals a 4:40 mile, which was a common distance for this workout. If you want to geek out on workouts, another regular one was 4X 60/90s (60 sec 400, 90 second standing rest).
As a humble middle distance walk-on, I was able to do the 12 X 30/30. My PBs in 800 and 1500 were WAY slower than the numbers being thrown around here. So it's not predictive of much, other than being a college-level middle distance runner.