Physiology will likely help none, and unless the 2015 MCAT is drastically different (could be), you should be able to study that semester without missing more than 5 questions (of 60) on that section BEFORE you finish class. Were I you, I'd at least study the other 2 sections all semester, then cram the last section, then take the MCAT on time. I wouldn't delay.
(Though I agree in principle with the above post.)