Agree with both above, you should train reps and holds, and one more option when doing pinch blocks, Saxon or the napalm blocks, try some wrist pumps when you lift, effectively you are trying to curl the weight up with your finger tips and using your wrist to curl up towards your body, this will help develop your wrist strength which is a huge factor for pinch grip type lifts and because it's dynamic, as in moving it will challenge you to hold on and you make gains in that way too... Super un technical explanation, but it's a great way to train 2-hand pinch