Browser cookies can have expiration dates for themselves. Most affiliate tracking cookies have a set time limit it will stay in the browser’s memory. Amazon’s affiliate cookie is 24 hours. That means after Amazon sets a cookie in somebody’s browser with your Associate’s ID stored, it will expire in 24 hours after the person clicked your link. That means you will earn commissions on items that a person purchases until that cookie expires. Many affiliate programs have much longer expiration dates set 30, 30, 90 days, or even more.