The muscles in the legs need the most time in order to recover, because of their size. This also goes for the muscles in the back, and in the chest. The muscles in the shoulders, forearms and stomach are a lot smaller and can be worked on a daily basis (after your body gets used to working out, of course). Your abs, or the muscles where your stomach is, are the fastest recovering muscles in your body.
Whenever I go to the gym, no matter which muscle group I'm trying to focus on, I always make sure that I have at least 2 abdominal exercises squeezed in there. The remainder of the smaller muscles in the arms always get a workout from whatever I'm doing at the time in the gym. When you perform your bench press, you're actually working all of the muscles in your upper body, but with more emphasis on your chest. Biceps, triceps, deltoids, pecs, etc... All from one exercise. You will, however start to feel the burn from the major muscle group you're focusing on.
Always have a plan when you go to the gym. If you want a full body build, then you should have a cycle to properly rotate which muscles you work on to give the muscles you're not working on adequate rest so they can recover. If there's anything you should take from this post, it's this: The point of working out is to break down your muscles, so they can rebuild stronger. While you rest, you rebuild. If you don't rest... You don't rebuild.
