Getting in a workout once a day is great, but if you sit the rest of the day, it won't help you lose belly fat. NEAT stands for nonexercise activity thermogenesis, and it's the calories you burn moving around throughout the day (not through exercise). Increasing NEAT will increase your metabolic rate, burning more daily calories, helping you lose weight.
If you work at a desk, make a point to get up and walk around a few minutes every hour, do some quick bodyweight exercises or stretches, take a walk during your lunch break, or walk up a few flights to get to the bathroom on a different floor in your office building. Using a pedometer can encourage more moving around and will challenge you to get in at least 10,000 steps.