I've been playing with UDP lately... you might be able to use the alarm function, like this:

# initialize your IO::Socket etc...
$SIG{ALRM} = sub { # code here to do something interesting 
                   # if your program isn't getting                    
+  
                   # connections
                  }
my $minutes_to_wait = 5; # wait five minutes
my $alarm_seconds = $minutes_to_wait * 60;

alarm $alarm_seconds; # set the first alarm

while($server->recv($msg,$MAX_LEN) {
     # if we're here we got something
     # do some interesting stuff with the message
     
     #reset the alarm
     alarm $alarm_seconds;
}
[download]

I put the server code in place but I don't have my client code in front of me to make sure the server doesn't execute that block even though its getting connections. In theory it should work though :) and if you don't receive something for 5 minutes it will execute the sig alarm block at the top.

Hope that helps.
Chris