The design of both OC's and OP's is supposed to make the exact release rate of an individual tablet irrelevant. After being taken for three days straight the pills traveling through the digestive system begin to produce a relatively constant serum level of the drug that is equivalent to what would be expected from taking 1/12 of the dosage every hour. With some people (such as patients with Crohn's disease, Ulcerative Colitis, ostomies, etc.. ), this steady state cannot be achieved by taking the drug every 12 hours and they are instead told to take a smaller dosage every eight hours.
Because of this, when a patient tells a physician that the OP's "take too long to kick in", the physician's training may cause him to suddenly become more alert to the possibility that the patient might not be taking them on the regular schedule he has prescribed. When there is a steady state, the drug is not supposed to "kick in" (or to put it a different way, it's always "kicked in"), so it's not expected that an oxycontin patient would think in such terms.
A good physician should consider other possibilities, however. For example, chronic diarrhea might result in tablets exiting too quickly to permit a steady state to be achieved with q12h dosing. Still, it can't hurt to be careful of what one says to one's doctor..
