Try to change your eating, healthy protein and vegetables. Stay away from sugar. Also, focus on High Intensity Interval Training. It will really help to burn fat around your tummy.
Give your muscles 1 - 2 days to recuperate from working out. So that’s exactly right, workout 4-5 days and take a couple days off. Also be careful not to work the same muscle group on consecutive days. Do upper body/abs one day, legs the next, then go back to upper body/abs on the third day.
First, Abs are made in the kitchen. You can do a million crunches per day, but if you are eating crap, you aren’t going to get the look you are going for. Truthfully, abs are 80% of what you eat and only 20% of how you exercise. Stick with super foods like Almonds and other nuts, bean and legumes, spinach and other greens/veggies, Oatmeal, Eggs, Turkey, Chicken breast, Peanut butter (but not too much), Whole grain breads, Whey protein, Fruits (but not too much bc of sugar content). STAY AWAY FROM CANDY/SUGAR! You say you don’t have much fat, so try to work out your abs intensely 2-3x per week using circuits to get a great abs workout in much less time. You don’t need to do ab exercises to get a strong core. When you work your legs you work your abs if you focus exercises like front squats with a barbell/dumbbell, dumbbell lunges, or even push ups you will see more definition in your abs.
I would say anywhere from 3 to 5 months depending on the intensity and how often you change up your workout. Also, eating healthy which you say you do. Cutting calories (but not too much) will help you reach your goal a bit faster, try to lose between 1 to 2 lbs a week to stay healthy.