This is a difficult question to answer broadly, given that every woman’s birthing experience is different. This means there is no hard and fast rule.
It all depends on whether damage was done to the pelvic floor muscles or connective tissue supporting the pelvic organs during birth. It also depends on whether you had a c-section, your previous exercise levels, and even whether you are breastfeeding or not. We know that some women can bounce back within weeks. However, others could take months to get back to their pre-natal levels of activity.
Having your pelvic floor looked at via internal examination with a physiotherapist post-partum is always a good idea prior to returning to exercise. A women’s health physiotherapist is going to be able to give you advice that is specific to you and the current state of your body.