Why delay coffee 90 minutes?

Delaying coffee 90–120 minutes after waking may reduce the afternoon energy crash by letting morning alertness develop before caffeine blocks sleepiness signals. 1

• Adenosine and caffeine: Adenosine builds while you’re awake and contributes to sleepiness. Caffeine blocks its receptors, masking that signal; when caffeine wears off, the accumulated adenosine may contribute to a stronger dip in energy. 2
• Let morning alertness rise: Cortisol normally rises near waking and supports alertness. Waiting to have caffeine allows that morning rise to occur; morning light and movement are also described as ways to support alertness and clear residual adenosine. 3 4
• Potentially less afternoon caffeine: Avoiding a pronounced crash may reduce the urge to drink more caffeine later, which can disrupt nighttime sleep. 5

The timing is presented as something to try, not a strict rule; caffeine closer to waking may make sense before early exercise. 6