These are refereed to as single, dipeptide or tripeptide aminos, depending on their length. These small aminos then enter the small intestine cells by crossing the outer cell membrane. In order to cross the cell membrane, receptor sites must be utilized. Intestinal cells are very receptor selective. Absorption will not occur unless the right length amino binds to the proper amino receptor site.
All receptor sites work equally fast.
After making their way into the small intestine the dipeptide and tripeptides are instantaneously chopped into single amino by internal intestinal enzymes. The single aminos are then dumped into bloodstream where the muscle cells will choose which single aminos they need. This increases protein synthesis which stimulates recovery and tissue repair or growth. As you can see, larger proteins such as foods, isolates or concentrates must go through additional sometimes lengthy digestive processes before making it to the intestinal membrane. And single free form aminos, although making it the small intestine rather fast, run into absorption delays in that they can only be picked up for transport across the membrane by single amino receptors.