Strictly speaking you burn fat best when in ketosis/fat burning mode. Or at the very least burn just fat. The way to get into ketosis is to deplete the bodies stores of stored glucise. This takes between 6 and 8 hours after eating. So finish eating before 9pm and by the time you wake (in the morning) you should be burning fat. Increase the amount you burn by training before eating.

It's possible to burn fat one day and build or at least retain muscle the next day by manipulating your carbs intake and your meal timing. Probably not ideal if you are mass building though.

Add in the health benefits of intermittent fasting and it's the perfect solution to fat loss.