I have read that you need to be off of the HC for a couple of weeks to get a accurate measure. Stopthethyroidmadness.com has info on this. What does your doctor suggest. I can't get the website to come up to get the link for you.
I'm on cortisol too and I've been told to do the saliva vials just before I take my cortisol. Same timing applies to all...
8:00am
12:00pm
6:00pm
Bedtime
there will be no change in dosing time, I would just collect saliva about 2Hr after taking HC which peaks in about 1Hr, more like 10am/2pm/6pm bedtime, what would be the purpose of testing cortisol levels while on HC then? I don't think it will solely show the body production of HC but I think it is useful to see how the body absorb it and metabolize it, to see if I would need more or less