As soon as you have enabled your Office Hours with your own custom hours you can choose the settings for the "Closed Call Rules".
Voicemail, here the caller is redirected immediately to voicemail.
Hangup, the call hangs up directly.
External number, please specify the external number and the call is redirected to this number.
Outside business hours message, upload your own .waw audio file and it will be played when your office is closed.