that timer you are creating as an "start event" is created in the working memory (KSESSION),
what is your runtime strategy?
SINGLETON: (Not recommended, but this would get your process instance fired in a kie-server, because the event wait will be created will be sort of global to the server).
PER_PROCESS_INSTANCE: This means that as soon as you create any other process instance, a KSESSION will also exist, which means that also your timer will fire).
PER_REQUEST: This will also get your timer to fire, although I am not sure about how your human tasks would work. (Please let me know the results of your observations on this one).
I believe that for your case, unless you can correct me if I am wrong, you should be using the PER_REQUEST runtime strategy to get your timers to fire.