Just to settle this argument, hopefully once for all.
If you are training strength you should never train the SAME muscles two days in a row (but to do upperbody one day and lower body the day after works out nicely). This because when the muscles are pushed to extreme they consume their own storage of carbohydrates and such, and therefore needs a day of refueling, and building the muscles you wanted to get from the training to begin with.
If you are going for endurance/stamina, than you go for a lower impact, and instead increase the time training, and the nurisment that gets transported to the muscles from the bloodstream will be enough and therefore you don't deplete any storage. Just train as often as you can.
When it comes to losing weight the later one is the one that can burn fat, but it's always a good idea to bulk a bit aswell, as an increase in muscle mass will increase how much your body burns even when not training.
Actually every other day is better. Though twenty minutes might not be enough.
They have proved the cycle in which muscles rest. On the first day after the excercise the muscle reach their absolute low point and working out again might do more harm then good. On the second day the muscles are recovering and strengthening themselves (caused by the previous work-out) and working out during that cycle will grant maximum effect.
Off course after three days the muscles have completely recovered and excercising again would not really be effective.