This test is the key follow-up to check your body's natural hormone rhythm. After peaking in the morning, your cortisol levels should drop significantly by late afternoon. This 4:00 PM blood draw is crucial to see if your levels are falling correctly. A high level in the afternoon is a key indicator of Cushing's syndrome (cortisol excess). This test is almost always done with an 8:00 AM test to provide the complete, dynamic picture of your adrenal health.