Abs are resiliant and technically you can work them every day, but theres no reason to. And they do need *some* recovery time. Legs actually need more recovery time than most other body parts, although you can do cardio almost every day (which does not count as "working" them, really).
Keep your body lean, your blood clean and your mind sharp. -Rollins
I've done ab workous where I've trained them 5 days a week around 20 mins a session. Then I've tried HIT, using weight and only 3 sets to failure once every 15 days or so. I've got the same results with both, I'd argue that I maybe have had a little better results with HIT. But bottom line there are many ways to train. Just fine a way thats suits you. However no matter how you train you need to rest your body at least once a week and you don't have to train often to get results. It all depends on what method suits you and motivates you. But with legs if you want to gain muscles you should not train them everyday, they are huge muscle and they need a lot of recovery time.
I know you are supposed to give each muscle group 48hrs of rest, but I've heard that you can work abs and legs everyday? Is this true or do they need 48 hours of rest as well?
When it comes to exercise in general, more is not always better. That's especially true when it comes to weight training. When you lift weights, you're basically causing tears in your muscles. When you rest, those tears heal and the muscles come back a little a stronger and/or bigger. But if you don't give them enough rest, then what do you think happens? If you're working a large muscle group like the legs, then you're probably doing things like squats or deadlifts. These are intense exercises that you can't do day after day. I personally never work a given muscle group more than once a week. Cardio doesn't count though cause you're tearing up the muscle. As for abs, I don't see why anyone would want to work abs more than 3 times a week. You use your abs in most exercises anyway or just during your daily routine when you're walking or sitting. So don't worry about doing lots of workouts for your abs and legs. It really isn't necessary and could be preventing you from making progress.
Usually legs need a day's rest but you shouldn't work them out everday. In fact twice a week, at most, will give you the results you need. Don't overtrain your leg muscles(or any for that matter), you'll be more at risk for injury.
Usuallly, after my leg day, I have trouble walking.
Me too. I usually do 3 sets of the Seated Leg Press, 15 reps each. Then 3 sets of the Leg Press lying down, 15 reps. Then 3 sets of Leg Extension, 10 reps. Then 3 sets of Leg Curls, 10 reps. Then 3 to 4 sets each of Hip Adductor and Hip Abductor, 12 reps each.