Before ttc, how long must I wait after stopping the Depo-Provera provera (medroxyprogesterone) birth control shot?

At least 3 months. Your last injection will be effective for at least 12 weeks of contraception. You can try to conceive after that. Depo-provera contraceptive can delay the return of fertility for up to 18 months. 90% of women without a prior fertility problem will conceive within 1 year of stopping depo-provera.