will it log only for the default time period
What do you mean by that? None of the rules that you add into a table will "expire" - you can rate limit using the appropriate rule.
or will it log all packets as they come in and out untill you # it out?
Every packet that gets to this rule (ie: is not rejected or allowed before this rule) will get logged. Typically, you would rate-limit the log message as follows:
iptables -A FORWARD --protocol tcp -o ppp+ --destination-port 2766 -m limit --limit 10/hour --limit-burst 5 -j LOG --log-level warning --log-prefix "Deadhat " iptables -A FORWARD --protocol tcp -o ppp+ --destination-port 2766 -j DROP
