What is the science behind this

Delaying caffeine 90–120 minutes after waking is proposed to let your morning wakefulness processes run before caffeine blocks adenosine’s effects; the goal is steadier alertness and less of an afternoon crash. 1

• Adenosine and caffeine: Adenosine builds as you stay awake and contributes to sleepiness. Caffeine competitively occupies adenosine receptors, temporarily blocking that signal rather than removing the adenosine; when caffeine wears off, sleepiness can rebound. 2 3
• Cortisol and morning light: Cortisol normally rises near waking and supports alertness. The explanation offered is that morning light helps produce this cortisol pulse, which can clear residual adenosine; taking caffeine immediately may block receptors without clearing adenosine and may reduce that clearance. 4 5
• Afternoon energy and sleep: Early caffeine may leave adenosine accumulating behind blocked receptors, contributing to an afternoon crash as caffeine wears off. Delaying intake may reduce the perceived need for more caffeine later, which matters because afternoon caffeine can disrupt sleep quality. 6 7
• Alertness, focus, and plasticity: Caffeine can increase alertness and focus. The discussion also connects delaying caffeine and getting morning light with strengthening circadian and cortisol-related circuits over time, while noting that good sleep is important for accessing neuroplasticity. 8 9