No, that won't work.
I think you are misunderstanding how GV works.
Ignoring OBi devices for the moment... When you set up a Google Voice account, and you obtain your own inbound GV phone number, you add one or more forwarding telephone numbers. By default (with no changes to settings), when an inbound call is made to your GV phone number, GV will ring all forwarding phone numbers for about 25 seconds. Whichever forwarding number answers first "wins the race". Either a human (you), or the voicemail system of one of your forwarding phones, is answering that call. There are two ways to alter this behavior:
If a forwarding phone's service provider supports Conditional Call Forwarding (also known as no-answer/busy transfer), then you would activate that feature, and have the carrier send unanswered or busy calls back to your GV number, where GV would take the VM message.
The "big four" mobile carriers (AT&T Wireless, Sprint, T-Mobile and Verizon) typically support CCF. Many service providers don't support CCF (most land lines and most mobile carrier low-cost subsidiaries or MVNOs).
So, in these cases, the problem is that the phone number(s) that don't have CCF enabled will grab the forwarded call to their own VM, instead of letting it go back to GV VM at the 25-second mark.
To prevent this, you can turn on GV's Call screening function. When this is enabled, GV requires that whoever or whatever answers the call press "1" to accept the call. Since your forwarding phone's VM system isn't human, it can't do that, and GV will take the call back to GV VM.
Phew. Now: OBi devices configured to use GV are actually using Google's old "Chat" system, and are simply treated as yet another forwarding destination, with the same call-handling behavior I described above. If the call is busy or unanswered, GV will take the message. No, you can't change the time interval for this.
Enable Call screening here:
https://www.google.com/voice#callsettings