pain

Hello all, I have inherited a panasonic kx-td1232 from a client to service for him. Now I am not very knowledgeable about phone system programing but I have 13 plus years in the telephony industry (i.e. I am a repairman/installer for a major company). The layout of the problem that I am facing is very simple as far as I can see. There are 6 system phones and 3 standard analog phones on the whole phone system. When a call comes into the phone system the 2 front desk phones (which are system phones) ring immediately and after the 4th ring the rest of the phones start to ring. The thing I need to change is that the client wants to change the rest of the phones to start ringing on the 3rd ring instead of the 5th ring. I have looked over the manual to no avail and I am completely stumped. Any pointers would be greatly appreciated.