Is is perhaps Ext. 10? The new Partner Messaging R1 has General Mailboxes of 9991, 9992, 9993, and 9994 for Auto Attendant 1, 2, 3, and 4. The Night "Dial 0/Timeout" option is to record a message in the General Mailbox for that particular Auto Attendant, and Ext. 10 is the General Mailbox "owner", and gets it's message LED lit until those messages have been heard.