Welcome to the RingCentral Community

Worked with several members of support staff to find a solution here, but we have it.
1. Build your call queue/voice group under ONE user, as a ring group. (Same effect as call queue, fully customizable.)
2. Disable "take messages"
3. On missed call, direct to another group/extension/IVR tree.

Hello Foxx Conner-Bailey,

I'm not sure what you mean by building a call queue under one user.  We already have numerous call queues set up for the different routing patterns on incoming calls; we want to be able to utilize the existing call queues as they are.

This should really be a native feature of the Group queues, which already have a "When maximum hold time is reached, send caller to..." feature.  Please upvote these feature requests and let's get this in RC.  Even crummy Comcast Voiceedge has this :)

https://community.ringcentral.com/ringcentral/topics/please-allow-calls-to-go-to-overflow-on-a-timer
https://community.ringcentral.com/ringcentral/topics/call-queue-should-overflow-if-agents-are-availa...
https://community.ringcentral.com/ringcentral/topics/ability-to-send-new-caller-to-unconditional-cal...

Thanks. The users are all extensions not numbers. Doesn't look like I can add extensions to a ring group as it's expecting full phone numbers. Otherwise that looked like it would have worked.

Luke - the issue is that the number cannot be an extension. It rejects it as an invalid number. It appears you cannot create ring groups from extensions as the field expects telephone numbers.
 

Hi SA 1,

You should be able to set up multiple Ring Groups in one user's Call Handling & Forwarding settings to accomplish this.

1. First, you will have to use the "Add Other's Phones" option to add all the phones that will ring in both groups. See step 7 in our Configure a User's Call Forwarding article for instructions.
2. Then you will have to create two Ring Groups as Taylor was showing you, see step 8 in the Call Forwarding article above.
3. Once you have set the time you want each group to ring before forwarding, you need to set up your voicemail options. See our article Setting up Messages & Notifications for details.
4. The last step would be to set up any email notifications you would like sent out once a voicemail is received. See the Notifications by Email section in the Messages & Notifications article for steps on setting that feature. 

Let us know if that helps you set up the call flow you want.

Add all of the numbers to the extension profile (not the ring group, but the numbers). Then, select the ones for the first group. Click 'Create Ring Group'. Repeat for the second.

Enable voicemail on the extension, with email notification.

Five minutes setup, tops.

Note: you'll want to keep the setting as 'sequentially' because it's going down the list of ring groups sequentially. If you change to simultaneous then the grouping here will be disregarded.