Automatically changing IVR based on time

[synthesis]

Hello. I am administering a Mitel 3300 ICP which has an IVR menu setup with a corresponding RAD greeting. I wanted to know if it is possible to change the IVR menu and RAD greeting depending on the time. For example, from 00:00-12:00 set IVR menu 1 with RAD greeting 1 and from 12:00-00:00 set IVR menu 2 with RAD greeting 2.

[Dogbreath]

If it's the voicemail IVR you're using then - I don't know.
If it's the ACD path/PIDL approach you're using, then yes.
Create your new IVR + RADs, test it.
Create a new number that has a Call Rerouting entry [eg a hunt group].
Configure the call rerouting on this new number to point at IVR A or IVR B depending on the service level of the system. If you're on MiVB8 or newer then you should be able to use Business Schedules to do this rather than burning night1/night2 on it.