From the OBiPlus Tutorial:
Day Time/Night Time Call Routing:
o In OBiPLUS, you may define your office hours (such as Monday – Friday, 9:00 am – 5 pm).
o In addition, you may define a number of holidays as exceptions to the normal office hours – for example: 1/1, 7/4 (US Independence Day).
o Any time during your office hours is known as Day Time; otherwise as Night Time.
o You may define rules to handle incoming calls differently during day time and night time.
I never used OBiPlus, so I can't help with the setup.