Based on the information available, Lipitor, a medication used to treat high cholesterol, typically begins to impact cholesterol levels within 2-4 weeks of starting the medication [1]. However, it may take up to 6 weeks to see significant changes in LDL (bad) cholesterol levels [2]. It is important to note that the full effects of Lipitor on cholesterol levels may not be seen for up to 4 months after starting the medication [3].

It is also crucial to continue with a heart-healthy lifestyle, including a balanced diet and regular exercise, while taking Lipitor to effectively manage cholesterol levels.

Sources:
[1] <https://www.webmd.com/cholesterol-management/lipitor-atorvastatin-oral/dd-lipitor>
[2] <https://www.drugs.com/lipitor.html>
[3] <https://www.drugpatentwatch.com/drugs/lipitor>