Today's arm workout incorporates pyramid sets again, so you'll increase the weight each set until you reach a six-rep max, then begin decreasing the weight each set until you reach 12 reps again. Between sets, restrict your breaks to 45 seconds.
The trick to maintaining momentum during pyramid sets is to have your weights laid out ahead of time. For curls, you might think about preloading the barbell with weights that you can easily strip off. You might have a pile of small plates around you at the midpoint, but who cares? You're just going to put them right back on.