1) EJB Timers are not intended to model fine-grained events. They are intended to model business process transitions on the order of minutes/hours/days. You can try with very small intervals but the throughput may not be great.
2) Unfortunately that's the only portable way to do it. This is one of the most requested EJB use-cases. We'll definitely support it in EJB 3.1. (
http://jcp.org/en/jsr/detail?id=318)
3) For a periodic timer, the next delivery can not take place until the prior one has returned. The expiration times are fixed at fixed intervals, but this is not a "real-time" service so that's merely a goal, not a requirement.
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