The timeout annotation is provider specific (weblogic, jboss, etc.). For example, for Weblogic it is @TransactionTimeoutSeconds(value=40)
http://docs.oracle.com/cd/E16764_01/web.1111/e13720/annotations.htm#i1438354
It's a class annotation, and should be put on the same class you have your javax.ejb.Stateless (or Stateful) EJB.
e.g.
@Stateless(mappedName="myClass")
@TransactionTimeoutSeconds(value=50)
public class MyClass implements ...