**Core Concept**
The question tests the understanding of the timeline of events in the menstrual cycle, specifically the timing of embryo implantation after ovulation. Ovulation is the release of a mature ovum from the ovarian follicle, while implantation refers to the embedding of the fertilized ovum into the uterine lining. This process is crucial for establishing a successful pregnancy.

**Why the Correct Answer is Right**
After ovulation, the fertilized ovum undergoes several cell divisions and travels through the fallopian tube towards the uterus. It reaches the uterine cavity around 3-4 days post-fertilization. The blastocyst, a stage of embryonic development characterized by a fluid-filled cavity and distinct layers of cells, is formed around 5-6 days post-fertilization. Implantation typically occurs 6-10 days post-fertilization, which corresponds to 7-9 days after ovulation. This timing allows for proper preparation of the uterine lining and synchronization with the developing embryo.

**Why Each Wrong Option is Incorrect**
**Option A:** 3-5 days is too early for implantation, as the fertilized ovum has not yet reached the uterine cavity and is still undergoing cell divisions in the fallopian tube.
**Option C:** 10-12 days is too late, as implantation usually occurs before this timeframe, and the developing embryo is already well-established.
**Option D:** 13-15 days is significantly later than the typical implantation window, and the embryo would be in a more advanced stage of development.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the timing of implantation can vary slightly between individuals, but generally, it occurs around 7-9 days after ovulation. This knowledge is crucial for understanding the early stages of pregnancy and the importance of accurate dating of pregnancy.

**✓ Correct Answer: B. 7 - 9 days**