This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
You could use the Timer service to call another class/method. However, a servlet's doPost/doGet require you to have an Http request open. Which you don't on a timer event. In other words, it would be more logical to call a non-servlet method. You could extract the logic from your servlet into a helper class/method that doesn't depend on the servlet API.