Well i don't understand why they test you at your highest peak. The levels obviously do not stay at this level for the whole day. I believe hey should take some form of average, or look at the lowest levels. One might peak out in the morning, and they rapidly decline and level out. Its at this point one would think that they would be interested in measuring.
It's measured in the mornings as per recommendations of the International Society for the Study of the Aging Male (ISSAM) and the European Association of Urology (EAU). Levels will always peak and trough and the trough is viewed as less important since everyone metabolizes it differently and the rate of decay or fall off is different amongst different people. Plus having the "accurate" testosterone value in the morning helps in determining if its primary or secondary hypo and the reference ranges given for the total serum testosterone panel are for the morning and take the diurnal rhythm into account