Why would you need to know that? Timers will be fired as soon as the session becomes active, even if the timer had passed it's origin fire time it will be fired as soon as session gets activated - that's called overdue timers. Timers do work properly with persistence, the only requirement for them is to keep session active.
That has been significantly improved in version 6, where use of quartz based timers is possible and even recommended in clustered environments.
HTH