How long would I need to gather the required number of packets to breakt he encryption?
I just wondered if anyone had ball park times for doing this in the real world?
Aspman, like XTC46 mentioned, it all depends on the encryption methods and the awareness of the administrator maintaining the system. If the admin uses WPA-PSK but chooses a weak passphrase, it could easily render the LAN prone to attack.

You may just want to sit down, pick a type of encryption and start checking out any/all wardriving tools/whitepapers related to that type of encryption. That's what I did in order to learn about WPA-PSK's weaknesses.