Do even the least bit of reading about lung physiology and function, and you'll see that the gas exchange and/or absorption of anything you breathe in occurs instantly. It literally occurs with the initial expansion of those little alveoli, the tiny air sacs where the chemical exchange occurs. Holding a hit doesn't do anything to make you higher, just like holding a breath doesn't do anything to make you absorb more oxygen from the air you breathe. In fact, holding a breath or hit likely hinders further absorption because it postpones the exhalation of the carbon dioxide and, in the case of cannabis smoke, other smoky by-products, which completes the emptying of the lungs and gets them ready to take another breath/drag.

If anyone can find anything saying otherwise, it'll be written by someone who knows nothing about the physiology of inspiration/expiration and will be completely bogus. The chemical intake occurs immediately. Holding hits just gives your lungs longer contact with the bad stuff, not the good.