You should try running for at left 20 minutes or bike around with ur bicycle for around 30 to 40 calories each dau. You can loose up to 500 calories just by biking or jump roping. That just depends on how long you do them and sometimes and what speed. But you shouldn't target on only yor belly. It won't help much that way, in my opinion.
You can't target just your belly when it comes to fat burning. You have to work out your whole body and eat cleanly. Cardio and strength training 30 minutes a day will definitely help. Not eating after dinner and drinking plenty of water also helps.