Can we set the Daytime Greeting by the day of the week as well as for the hours?

Yes. The automated attendant has three greetings that can be used. 

You can specify what the daytime hours are for weekdays and you can specify what those weekdays are. You can create a greeting that plays to callers during daytime hours and another that plays at nighttime.

Anything else is considered a weekend and you can also record another greeting that plays on weekends.