I have been trying out different Bi and Arms rep and set schemes the past couple months for the after layer workout Bi and Back. I have been using straight sets, clusters, reg HDL and so forth for different cycles.
Lately CT has recommended straight sets and anything below 15 minutes is fine, just get the load and work in...keep it simple.
I've been getting good results with this: For example Bi's...I choose a weight where I can get 6-8 reps the first set. Then repeating sets, as the work increases I terminate the exercise when my last set gets down to the 2 reps completed range.
This work takes about 10-12 minutes inside the 15 minute window and it's working well.
"Lets get nasty"