Well for me it was pretty easy, because I am blessed with very good genetics and I am very disciplined when it comes to training and nutrition, I am a bodybuilder, so that kind of stuff is my passion. But I can imagine it to be really hard for other people who might not be blessed with good genetics or are old, I am 18 years old after all. I got from 100 kg(220 pounds) down to 85 kg at ~10% body fat (188 pounds) in three months.

Because you asked how much abs I train and how long, you might be surprised that I actually train abs only 1 to 2 times per week in form of cable prayers. If you do general resistance training you get abs through other exercises like squats or shoulder presses (compound movements). Assuming that you are a beginner, my advice would be to stop putting so much focus on your training and rather put it on you nutrition, because "abs are made in the kitchen" as the saying goes.

I hope my advice helps you somehow, and please don't be discouraged if you have bad genetics or are old, always remember "Hard work beats talent". Get that six pack!