I take my son who is 4 in the morning. My endo said that it does not matter what time of day. But when I called the Lab to see if they drew the 21 hydroxally, plasma renin and activity something they told me to come first thing in the morning so i asked my endo and she said that it did not matter so i just take him in the morning anyways. I also give him his cortef before i go . Misty