you would have to change the ringing to go right to the auto attendant when in day mode. That would be a pain to go back and forth.

You can record greetings 0 through 9 in both day and night, so you could have a second or third greeting in night mode to reflect the day to day situation, it's easier to frog from greeting to greeting then mess with the ringing. Then you can put it in night for immediate answer and have whatever greting play. Does this help?
Mark