They say 6-8 weeks, but it can take up to a year for all your insicions, nerves & muscles to heal completely. It's best to take it very slow & gradual when it comes to working out your abs or doing any exercises with binding or lifting weights in a way that you will somehow affect your abs/hip flexor area.
Personally, I waited until after 6 months because I was still in noticeable pain at the insicion area with slight tingling. I really starting working out full force about a year after. My daughter is almost 15 months now and I no longer have any pain or tingling (besides the occasional ghost pain). I did have to change my workout a bit since I am now about 15 weeks pregnant, but it's really up to your body's speed of healing and not working yourself too hard too early.
I think it is 6 to 8 weeks depending on your doctor.
I have 2 c sections but I never worked out afterwards. But I must say that I feel like I am back to my old self after 3 weeks. I can do light house chores after 1 week so to me that was a work out. :)ask your doc to be sure but I think the general guidelines is 6 weeks.