This is probably the ultimate question when you're choosing a workout program. It really depends on your fitness ability, diet and plain old genetics. There's a whole spectrum of results that can be achieved from working out. Some people will see these results quickly and some people, it will take more time to see results.
In general within the first 1-2 weeks, you'll notice a little more heart and lung capacity compared to when you're first starting out and even a little more strength provided that you're working out 2-3 times per week and that you're fueling your body with the nutrients you need to power through the workout and to lose fat and preserve muscle.
When you decide to sign up for a fitness program, you're making a decision to change your lifestyle all together. Could you make short term gains and get ready for that tropical island trip or wedding within 12 weeks? Sure. Again, it really depends on the fitness program you choose and how hard you're willing to work for what you want.
Rest assured that we're to help you every step of the way to a stronger and healthier you!