> In athletes, it is known that endurance performance is poorer early in the morning and late at night compared with the afternoon [6], and that MFO and Fatmax are higher in the afternoon compared to the morning whether in non-athlete male students [7], in untrained normal-weight and obese individuals [8], or in endurance-trained athletes [9]. The difference has been explained by the higher body temperature, the enhanced neural activation and contractile properties of the skeletal muscle, and the higher plasma catecholamine concentrations found in response to exercise in the afternoon compared to the morning and evening [10, 11].
So it seems like regardless of if you had caffeine or not, it is better to work out in the afternoon vs. in the morning