The number of rings before the automated attendant is controlled by the phone system, not the voicemal.
If you have a Partner ACS, R3 or later, it is #506-(1=Day/2=Night)-(Line Number)-(Number of Rings from 0 to 6)
If you have a Partner Plus, Partner II, or Partner ACS R1 or R2, it is #506-(1=Immediate or 2=Delayed)
AND, Immediate is 2 rings, Delayed is 4 rings, because Caller ID comes in between the 1st and 2nd rings, and the designers wanted you to be able to capture it if you have that feature enabled.