[Click] question on element scheduling

[Indian Mogul]

Hi, 
   I have a simple question for which I have been
laboring for quite some time. 
In my router config file, I want one of my click
element to periodically check for the value of TTL in
the table irrespective of whether packets are recvd or
not? The name of the element is check_ttl() and the
path where it is introduced is:
//Fromdevice()->classifier->get_flow_id()
  ->check_ttl()->//

so, inside the element I have code that does:
// Check current time.
// If (current_time > expiry time)
//    flush_the _entry
//   else 
//     do nothing. 

1. Now, my question is, will the element "check_ttl()"
get automatically scheduled at the right time
irrespective of whether packets are there or not?

2. Since click is single threaded, how do I schedule
the check_ttl() if ans to (1) is false?

Thanks?
IM

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