How long does depo provera shot take to kick in if it is not given during ovulation nor period?

Weeks: Many OBGYNS suggest you use a backup form of contraception (condoms etc.) for 3-4 wks if this was your first dose. It likely is effective earlier but the overlap is a safe precaution. If this is an on time followup dose it maintains the existing protection immediately.

Depo provera: It's best to continue using condoms or another method of birth control for the 12 weeks until your second depo provera shot. Condoms are also best for protection against STIs.