When not on exogenous testosterone, you have to check T levels at around 8 in the AM, because this is when they peak. Yes, later in the day it will be lower, so that makes sense. You can calculate free testosterone by using the Total, SHBG, and Albumin. There is a calculator online, just type in Free Testosterone Calculator.
This is where doctors are retarded when it comes to testosterone being on the low end. Ok so you have 300-400 Total test, at 8AM, but as the day goes on, these numbers go down, so what are you at 4pm? 200? 100? . When you try and explain this to a endo, or doc, some will get it, and some will say “Well you are in normal limits” “Your normal” Which is complete garbage.