Change Number of Rings Before Voicemail Picks Up
Call Forward Variable lets you customize the number of times your phone rings or the length of time elapsed before the call is forwarded to your voicemail.
The number of seconds before forwarding can be determined by multiplying the number of rings by 5. For exampe, 6 rings x 5 = 30 seconds before forwarding.
There are two methods available, so try both to see which one works for your device.