Hi TCF,
We encountered this exact issue. We are using the 3CX Version 15 Enterprise edition and had a need to have multiple primary inbound lines with different office hours. To be consistent in every case, we created a dummy extension in a logical numbering range (for us 1000-1999). We assigned the primary DID for our main line to this extension. We would then set specific available hours on the "Fowarding Rules" page. During the "Available" status hours, we would permanently forward this dummy extension to a Digital Receptionist IVR, or directly to a queue. Outside of business hours, the dummy extension would automatically flip to "Do Not Disturb" mode. For this status we set forwarding rules either to another queue, or IVR with out-of-hours options for the caller to choose from. We would then place an option in the out-of-hours Digital Receptionist to transfer to voicemail of the dummy extension. This extension is populated with the email address of where would like the voicemails to be sent to. We change the voicemail options to the dummy extension to send voicemails directly to email and skip the voicemail box.
This all sounds complicated, but when you understand the workflow it actually gives you a much greater degree of control.
Send me a PM if you'd like to chat more about our scenario.
Thanks,
Erik