esoare,
There isn't an automatic Day/Night mode on any version of the software.
There is however a Schedule Time-Based Application Router that would probably do what you want it to.
You can find that in Voice Processor > Devices > Applications, and I suggest using F1 to read about it.
If you use a STAR for this, you would send the calls to the STAR first and let it determine what to do based on time.
As for your solution, that would work too, for as they say, "there is more than one way to skin a cat".
Thanks,
TE