90 minutes after you're supposed to wake up based on your chronotype—that's when you should have your caffeine. The reasoning is because cortisol and adrenaline have boosted you up to wake you up in the morning, and so when you have that those two things functioning in your brain, adding caffeine does almost no good ... Cortisol and adrenaline are like cocaine compared to caffeine, which is like weak tea, in terms of just how powerful they are towards the brain.