It's known but not well understood that heart attacks are more common in the morning, and more frequently fatal. Dehydration is considered a factor. Other theories exist; some could affect performance.
A google search on athletic performance at different times of day finds results indicating late afternoon or evening are ideal.
IOW, morning suck, as we all knew already. Coffee as a morning stimulant is legit.
Compare morning performance to morning performance; leave evenings out of the equation.