If your using mIRC you shouldn't need to know, that notice is sent in parrallel to a PING request from the server, mIRC automatically replies with a matching PONG request. You would only be pinging out if you or the server are extremely lagged or something is broken (a psybnc maybe).
The ping/pong on startup exists to prevent ip (and consequently host) spoofing from occuring and also stop some of the more stupid drones, if the ping didn't exist the entire client registration process to the server would be one-way, allowing kiddies to forge packets from any ip address. For this reason the ping is made very hard to predict.
Hope that helps.