I need to pass in process variables map into a process that is kick-started by a start-timer event. The process seems to be started as soon I deploy my DeploymentEntity ( as noted in the document ), that I don't get a chance to pass in my params via RuntimeService.startProcessInstanceByKey(key, params).
You typically don't want to provide variables when using a timer start event. If you need some data in your process, you can simply attach an execution listener that adds those variables.