There have been many competing camps as to which time is the best to workout. Some will tell you that to lose weight, it is best to workout in the morning. You do not have the fuel from breakfast, so your body turns to the stored fat for energy. You then burn more fat, and this primes your body for an increased metabolism throughout the rest of the day.
The other camp says you should workout later in the afternoon or evening because your muscles have been warmed up from the day, and you will have more energy to perform the exercise which will mean more of an effort and more energy expended. More weight on the bar or pushing yourself that extra mile will help you achieve your desired effect more quickly.
I can see the logic behind both camps but I would like to offer a third option: It really doesn’t matter! Weight loss is primarily based on your body’s ability to burn more calories than you take in. It isn’t as much a question of when you exercise, just that you do something every day so you expend more calories than you take in.