cortisol adrenal side effects

These are my labs done at 530pm. Normal cortisol at that time ranges from 3-10. Mine was 2.9. Ran a MRI for Pituary Tumor came up with none present . Now Endo wants to run a cortisol stimulation test to rule out adrenal insufficiency before puts me on TRT. Could this just be cuz the time of day...

I was diagnosed with lower-than-normal cortisol about a year before starting TRT. This was not your standard blood test - which can bring erroneous results. This test was a "saliva test" which means that 4-5 times a day, I had to spit inside a tube, and then have that tube shipped to the lab...