RE: when to train grip & forearms?
I just pick 3 session to throw 10mins extra in to train it, unless you are looking for strongman type of gains and progress I don't feel there whereabouts in your regime matters too too much.
After Chest and Bis I do thick bar static hold and lever work. After Legs I simply do some flexion grip work (for want of a better phrase). After Back I do pinch grip work.
So far so good.