Forgot "void" on rotate() when typing in the example but the actual problem is a null timerService variable, as stated.
TimerService on 3.0 entities are not supported.
From JSR 220: Enterprise JavaBeans TM, Version 3.0, Final Release, Chapter 18.2 2nd paragraph:
Timers can be created for stateless session beans, message-driven beans, and 2.1 entity beans.
Timers cannot be created for stateful session beans or EJB 3.0 entities.