I am using the Obi202. The obiplus project wizard has a "Day Time AA" and a "Night Time AA" under "Auto Attendant" - as well as a place for office hours.
Here's what it says under the help tab:
"OBiPLUS offers two AAs, one for day time and one for night time. You can enable either one or both according to your needs. For an AA to work properly, you must record one or more prompts on your main OBi and apply them to the AA."