I think I was riding about three weeks after delivering DD. Nothing fast or strenuous, but I was able to get on my townie bike and do a couple of errands.
It totally, totally depends on how your delivery goes.
Just trust your body when it comes to getting back to things, and take it easy on yourself! It won't be the same for a while!
2007 Trek 5000
2009 Jamis Coda
1972 Schwinn Suburban
"I rejoice every time I see a woman ride by on a bike. It gives her a feeling of self-reliance and independence the moment she takes her seat; and away she goes, the picture of untrammelled womanhood."
Susan B. Anthony, 1896