I’ve had doctors tell me that it doesn’t matter when you do the blood test.  I once showed up 3 hours before our appointment to make sure my son had the blood test done as early as possible (I think between 8:30 and 9:00) and sure enough, the doctor said his levels were up that time.  They told me to give him his medication I think one or maybe two hours before the blood test.  I also have him fasted but I’m not sure that makes a difference.