The pharmokinetics of the blood plasma levels of the drug is one thing, but the drug in question is an anabolic steroid. As is alluded to above, the mechanism of action of anabolics is to enter into the cell nucleus and upregulate transcription of mRNA and hence proteins. This is a process which is not instantaneous. We're not talking about a pyschoactive substance say like valium which has a more direct mechanism of interacting with cell surface receptors and changing ion gradients. Transcription and translation (making new proteins) takes time.