I do one day a week with some direct ab work usually 3-4 sets. One week I do my "light" phase the next week I do my "heavy" phase. I do between 8 and 10 reps in each set. Used to do two days a week where I did one heavy and one light but with all the squatting, deadlifting, overhead pressing and various event training I do it was too much. I also don't give two shits if my abs are visible or not (currently not) the only reason I train them directly is for more core stability.
Of course what do I know I'm just one of those "Fat powerlifters".
Cheers,
Scotsman