@chai2,
Chai,
Your question is answered in the link I posted.
With a little experience of your own body reactions, you can track your circadian rhythm.
Let's say you have a migraine during the night.
That's almost useless to take a medication for that between 3 and 4:00 AM.
But if you take it by 8:00 AM, its efficacy is maximum, if you circadian rhythm is normal.
If it's delayed cause you don't sleep at night, experience will tell you how many hours delay you have...