How many HIIT workouts should i do during 1 session?



I want Abs SOO BAD! I've been doing a couple of workouts trying to figure out what my routine is going to be and I was wondering how many HIIT workouts should I do during one long session of working out? I just really want a flat stomach, Sometimes I'll do a 2-3 videos of HIIT (about 45mintes) of pure HIIT Ab training. Is this a good thing? I just wanted to make sure I'm not over-doing it because after my HIIT ab session I usually do at least 1-2 low intensity ab training as well. So usually I am working on my abs for 1-2 hours every other day. I usually do HIIT sessions 2-3 times a week.