Exercising in the afternoon would mean exercising after lunch. It's best not to exercise too soon after eating to avoid nausea as the blood in your body works at digesting your food instead of taking oxygen to your muscles. So an afternoon exercise would be done at around 3 pm. Most people who work wouldn't be able to fit this in with their working day.
However if you're available at 3 pm and you choose to exercise then the gym is not usually busy at this time. They'll be no queuing or time limits for the treadmills. It gives a nice split in the day and you can carry on working after your exercise. You're fully awake at this time and your evening meal will be able to fill the hole that the exercise gives unless you take on some protein.
This is when most people exercise. When you finish work you get on the treadmill and do your evening workout. You won't have eaten for a while, you will just have an evening meal after your workout in the evening to replenish your energy stores. It's the most convenient time of day and gives you the remaining part of the evening free to spend with the family
The problem is that after a day's work sometimes the last thing you feel like doing is going for a run on a treadmill. A body that's already tired may not get the best of exercising. However they very fact that you may feel sluggish means that exercise will wake you up again and give you energy and an increase of happy hormones for the rest of the day.
Any exercise is better than none
You can have research that proves the morning is probably the best for exercising when it comes to the human cycle. However all the research points to the fact that whenever you do the exercise, the fact that you are exercising is very good for you. If you work during the day then we're not finely tuned athletes so as long as we get the exercise in there, then there is a lot of benefit to us.
The CDC says you don't have to do your exercise all in one go. You can do it in 10 minutes chunks and still get the benefit. Now most of us will exercise longer than 10 minutes at a time but it still shows the nature of exercise and it's benefits. So in conclusion the research says morning is best, however, as long as you get it done on a regular basis it doesn't really matter what time you do it.