It’s up to you, what timings suits you and makes you feel comfortable to exercise. The physiological effects of exercises remain same no matter when you exercise. But along with you your body should be in state of exercise. Usually, afternoon timings will be lunch time so, exercises are not recommended just after or before lunch. So if you are doing your exercises make sure proper gap is kept between the lunch and workout. Also the environmental factors need to be consider if you are going for outdoor physical activity or exercises. To get maximum benefits from your workout be regular with your exercises.