This paper suggests 10 repetitions of 1 min exercise and 1 min rest. I've never been able to manage that myself - I wimp out after about 6 reps. (What's going on here is that you are depleting muscle glycogen levels in a manner that's relatively heart friendly - basically 30 sec or 60 sec of exercise isn't enough for the heart to reach maximum rate).
The evidence for lowering LDL with HIT is actually kind of mixed. But there are consistent improvements in hypertension, insulin resistance and glucose levels - and if you can't control LDL, then keeping those under control is even more vital.