The recommendation to get a testosterone value early in the morning is because levels start to drop after 10 or 11 a.m. However some recent studies showed little change in blood testosterone levels in men 40 and older over the course of the day. One reported no change in average testosterone until after 2 p.m. Between 2 and 6 p.m., it went down by 13%, a modest amount, and probably not enough to influence diagnosis. Most guidelines still say it???s important to do the test in the morning, but for men 40 and above, it probably doesn???t matter much, as long as they get their blood drawn before 5 or 6 p.m. As for men already on trt it shouldn't matter at all except I would recommend to run labs at similar times and day relative to your injections in order to tract levels consistently.