How strong is the evidence for Caffeine Timing?

A randomized crossover trial directly tested caffeine dose and timing before bed and found it prolonged sleep latency and reduced total sleep time in a dose- and timing-dependent way, and this is reinforced by a systematic review of caffeine and sleep across epidemiological and randomized studies reaching similar conclusions. That evidence is currently rated moderate (47/100), built on 3 published studies, including 1 randomized controlled trial -- a reasonable base, but not yet enough for full certainty.