How long until I can exercise after explant?

You need to ask your surgeon this question since he/she knows exactly what was done to your tissue. Most women can resume full activities at 6 weeks.

Most patients are back to normal day-to-day activities such as driving a car in 3-4 days. To be on the safe side it is probably best to restrict upper body movement for a total of 3 weeks postoperatively. Heavy upper body exercises should probably not be resumed for 6 weeks. These guidelines depend on the healing process in your particular situation. It is best to follow the directions of your surgeon regarding your restrictions during recovery. Good luck

You need to ask your surgeon when you can go back to activities.  In general, I prefer patients waiting 3-6 weeks for most activities.