I wasn't too overweight ( well I wasn't overweight really - just a bit too much belly/body fat).
To get top two sets to show along with general ab outline was 3 or 4 weeks from memory - next set down was again about 4 week from then - next set down slight outline next few weeks ( never has been defined properly). I'm male so its probably easier than for females.
I found I needed to put on muscle as cutting that low in body fat left me feeling I was underweight ( and in doing so you loose muscle too - unless maybe if you're on a steak and eggs only diet)
It's winter here now where I am ( not swimming weather ). I am now intentionally overeating ( primal foods) and lifting heavy - muscle bulk has increased and so has body fat percentage but still the top two sets of show along with general outline of the area. I've put on about 12 pounds of weight, of that is probably about 4 pounds of fat (waist size has not increased - a good thing). In any case I don't have a fully defined ab section but I'm happy with my current composition over the winter and will keep eating big and lifting heavy for a while.
Was it worth it ? : depends on the sacrifices/effort to get them , sacrifices/effort to maintain, the benefits you see in having them ( eg you live in warm climate near the beach and you like to show them off whist swimming etc - again subjective.
See the steak and eggs thread to reduce body fat - maybe there's something in there for you.