Long Timed Sets

I have a question about long timed sets as a supplement to training.

Right now I’m powerlifting, concentrating my workouts on heavy weights and speed work. The workouts are already on the long side, the movements are very powerlifting-specific, and the workout is fairly taxing, but it don’t include any bodybuilding movements (besides some basic pulling movements), which I’d like to balance things out a bit better.

I’m thinking about adding some isolation work, but I want to keep it minimal to keep it from interfering with my lifts. If I added, say, 3 minutes of an isolation movement into each workout, how would you recommend getting the best bang for my buck?

I’m leaning towards timed sets rather than set-rep schemes just so I can keep it short and focused. Should I do a three minute long killer set? Two 60-70 sec sets (with 20-30 second rests in between them)?

By the way, I’ve enjoyed your growth factor workouts in the past. Right now though, I’m in a home gym with mainly barbells and bands. The GF circuits seems to work best with a variety of equipment around, so I suspect I’m going to have better luck with single movements.