About a month for me. After my incision was feeling better, I would lay on my back and tighten my stomach muscles as hard as I could and hold for as long as I could. I saw a difference in a few days.
And you look absolutely amazing for having two kids, and being 3 weeks PP.
it doesnt actually ever close, unless you have surgery. it can go back together, but the seperation is still there. i got it with my second... its a bitch lol
i've been religiously doing transverse abdominal stuff and i see a huge difference so i'm hoping the gap comes together relatively well. hate the postpartum time!