This is a very frequent question, many people ask me what is the best time of the day to burn fat or increase muscle mass. The truth is that your body will react to the stimuli you give it during training no matter what time you workout, as long as you perform exercises correctly and at the moment you can do your best.
I’ll explain myself better, if your daily routine makes you go to bed late, training very early in the morning may not be the best for you, you are probably gonna be sleepy and without energy and it is important that you give your body at least 7 to 8 hours of sleep. But, if you always wake up early and your day is very busy, exercising early suits you because it will prevent you from skipping later on the day because another important thing came up.
Every one is different, some people love working out in the morning because exercise increases your energy, productivity, concentration and creativity, doing it early will help you in all aspects of your daily routine. However I can't workout before 9am, I have zero energy I feel I'm dragging myself over the gym and don't get a good workout, so a bit later works better for me.
Exercise also releases stress, if you finished working, did errands, etc., exercising will help you release the tensions of the day.
Exercising in the morning usually helps you connect with the healthy wave and eat healthy all day, allowing you to keep up with the steps to lose fat or increase muscle mass. On the other hand, studies indicate that in the afternoon / evening cortisol levels are lower and testosterone levels are higher, which can help you build / gain muscle mass and lose fat.
Beyond studies or recommendations you should include exercise in your daily routine at the time that is most convenient for you, at the time you can perform better, when you have the energy and willingness to do so, in that space of time you created in your day to do something for your health and well-being.
The best time to exercise is when you can!