See the DrugPatentWatch profile for lipitor

Based on the information provided, I cannot directly determine when Lipitor will start improving joint flexibility. Lipitor, a medication commonly used to treat high cholesterol, does not have joint flexibility as a listed benefit or side effect. It is primarily used to lower the risk of stroke, heart attack, and other heart complications in patients with type 2 diabetes, coronary heart disease, or other risk factors [1].

If you have observed improvements in joint flexibility while taking Lipitor, it may be coincidental and unrelated to the medication. If you have concerns about joint flexibility or any other health issues, it is recommended to consult with a healthcare professional [2].

Sources:
[1] <https://www.webmd.com/drugs/2/drug-14/lipitor-oral/details>
[2] <https://www.drugpatentwatch.com/drugs/lipitor>