Somewhat depends on which voicemail platform you're using. During day, you probably have lines overflow to Hunt 450. In night, you will probably want lines to ring to VM hunt (usually 440) and send a VMID that launches a night auto attend. You'll find most of this in FL 40 programming. If using the Flash based platform, maybe have a digit on day menu (i.e.8) launch night menu - then have CO line VMID be 8. You may need to use some trial and error testing. If the hard drive platform, you can set CO line VMID to an unused mailbox, then have that mailbox launch the night greeting.