Thanks for your feedback.
If I'm understanding your query correctly, you would like to silent your device from receiving any 3CX notifications/calls.
You have 4 options
1. Enable Silent mode in the 3CX client. You will still receiving calls/notifications, but will not ring your device
2. Set your 3CX extension status to Do Not Disturb. You can also set forwarding rules for this option.
3. Set your device to Do Not Disturb from your Android native settings
4. Configure office hours for your extension