**Core Concept**
Acute graft rejection is an immune-mediated response that occurs when the recipient's immune system recognizes the transplanted organ as foreign, leading to an inflammatory response against the graft. This process involves the activation of T lymphocytes and the release of cytokines, ultimately resulting in tissue damage and graft dysfunction.

**Why the Correct Answer is Right**
Acute graft rejection typically occurs within the first few weeks to months after transplantation, with a peak incidence around 7-14 days post-transplant. This timeframe is due to the initial activation of the recipient's immune system in response to the presence of the graft. The activation of T lymphocytes, particularly CD4+ and CD8+ T cells, plays a crucial role in the initiation of the immune response. The release of cytokines such as IL-2, IFN-γ, and TNF-α further exacerbates the inflammatory response, leading to graft damage.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because chronic graft rejection typically occurs months to years after transplantation, rather than within the first few weeks.
**Option B:** This is incorrect because hyperacute graft rejection occurs within minutes to hours after transplantation, due to pre-existing antibodies against the graft.
**Option C:** This is incorrect because this timeframe is more characteristic of chronic graft rejection.

**Clinical Pearl / High-Yield Fact**
It's essential to note that acute graft rejection can be prevented or delayed with the use of immunosuppressive medications, such as calcineurin inhibitors (e.g., tacrolimus, cyclosporine) and corticosteroids.

**Correct Answer: B. within minutes to hours after transplantation. Hyperacute graft rejection occurs within minutes to hours after transplantation, due to pre-existing antibodies against the graft.**