I do mine on the trainer paced based on cadence and perceived effort. My trainer resistance is pretty consistent after the first 10 minutes and I mount the bike with the same number of turns and have the tire at the same pressure each time. Having done this enough times, I know that in a specific gear at a certain cadence, I can barely maintain the effort to the end. And then I add one more rpm for the next set.

For me this is mentally taxing enough. The thought of doing 5 consecutive 30 sec all-out efforts would make me reconsider why I ride bikes.