What product are you talking about John?
Usually fat burners are taken before breakfast, say 15-30 minutes pre breakfast if possible.
Most fat burners are tough to split in half too...
If you take a fat burner before your early pre work workout, you'll have more energy and likely a dash more fat burning benefits (some ingredients help free fatty acids, which you gotta burn during workout time)... but then it'll wear off earlier on in the day too, so you have to consider timing of the second dose. Depends on what you're using and when you have breakfast...