When's the best time to workout? Anytime you are willing to! A more scientific answer would be between 9:00-11:00am when cortisol levels are highest. The stress hormone cortisol not only keeps us alert, provides available energy, but it has an anti-inflammatory effect on the damage produced from the workout. For those with inflexible schedules, test out this time during the weekend and shift your weekday workout to either 6:00-8:00am or Noon to 1:00pm.