Your postpartum checkup is usually around 6 weeks, but guidelines are changing and sometimes your physician will see you sooner. You can start doing P.volve as soon as you are cleared postpartum for exercise by your physician.
If you have been doing P.volve during pregnancy then you should have no problem going right back to it since it is low impact. However, you may want to modify for the first week or two until you feel stronger. As with any exercise, you should not do it if you experience pain.