There’s no one time to exercise for weight gain that produces better results. The best thing to do is focus on training at the time of day when you feel most energetic and that fits your schedule. For most people, this is in the mid-late afternoon. Sessions around this time are fuelled from the day’s eating, and you can usually switch into ‘recovery mode’ afterwards with food and relaxation. However, what matters most is fitting your training into your day and your recovery schedule.