How 2 switch a hunt group to a night service or v/m?

[Zu56]

Hi all,
Definity G3si ver.12
I have HG on time table going to an answering service, but sometimes they need to switch it to a local v/m for a short period of time.
The hunt group screen has a night service field in it. I assume that I can switch the HG to some ext. and back. Does anybody know how to do this? And will this be the best way to do what I (they) need?
Thank you

 

[busster]

Assign hunt-ns button and define night service.

 

[Zu56]

Thank you.