If you look at the documentation (docs.microsoft.com), you will find examples on how they use -TimeOfDay. Seems like you are on the right track.

By what I can tell from the documentation, there will be no options presented to the caller if you don't set a -KeyMappings. -KeyMappings default to $null.

https://docs.microsoft.com/en-us/powershell/module/exchange/unified-messaging/new-umcallansweringrul...