How long do cannabinoids affect receptors after smoking?

The web site mentioned by the previous responder did not, to my knowledge, answer the question.  The answer to your question is that cannabinoids will only affect the CB receptors for a brief time.  This time will depend on the concentration of delta 9 THC, but it will probably be on the order of minutes after cessation of smoking.  Now, the downstream effects (second messenger alterations) will last much longer, but that wasn't the question.  The off rate for THC is fairly rapid, so the actual receptor will not be affected for very long.