how do I lengthen call time before the answering machine starts?
The only thing programmable within the VM settings are:
1. if it is enabled or not and
2. the duration of how short or long the VM itself will be.
3. The greetings which are invoked after reaching VM
VM is activation is based upon the rules established for the extensions that sent the call to the VM. Once a call is sent to VM, the VM function is invoked immediately; otherwise the caller would hear dead-air and possibly hang-up not knowing what happened which defeats the purpose of having VM.
So, if the rules state call forward busy to VM, if the extension is busy, off to VM it goes.
If the rules state call forward unanswered after 20 seconds to VM, then at 21 seconds of ringing off to VM it goes.
If a ring group default is to VM and all members are busy on a call, off to VM it goes.