Puppy time out length.

I don't no where I read this, it could be from this website or the Jack Russell for dummies book but its regarding time outs for my 11 week pup. I understood that when my puppy just won't stop a behavior such as biting hard for attention even after repeated times of trying to distract him or telling him enough he continues, I give him a time out in his crate until he calms down and stops barking.

I do this for approximately 15 minutes and every time he comes out quiet and friendlier. Could be the treat that I give him for being so nice and quiet. BTW, I've only started giving him time outs after he 8 weeks and 3 total.

My question is, we started puppy class at a local Petsmart and the trainer insists that 30 seconds is enough regardless of his whining or barking. Is this correct and have I been doing this wrong this whole time? Are JRT behavior training any different than other puppies or is this trainer misinformed?

I included a link of a previous question similar.