Titchou is right. You will need to eat more to keep from losing weight. Ideally you should have either juice or a sports drink 30 minutes before you jog so that your body will have higher bloodsugar and calories to burn during the exercise. 6-8 oz. should be enough to fuel your exercise without making you feel full or bloated. Then you need to eat as soon as you're able once you're finished. This will help replenish your body's glucose and glycogen so that you will be less likely to lose more body weight.
In 20-30 minutes of moderate intensity cardio, you're probably not burning more than an additional 300 calories or so, so including that much more to your diet is all you really need to do to maintain.
The time of day makes no real difference. Just go when you're most comfortable exercising.