You can have multiple AA greetings based on time but in basic you can't specify monday-friday only the times to be used 7 days a week. It kind of depends on how you want the system to work but generally use a single auto attendant for day and night message. If you need another greeting beyond that typically another auto attendant would be used. However, if you are ok with the limitation on time profile in basic, you could use just one auto attendant.
Example1) A restaurant open 7 days a week 24 hours a day
morning greeting says we are now serving breakfast
afternoon greeting says we are now serving lunch
evening greeting says we are now serving dinner
the menu options says what to hit to get call routed
Example2) Business open 5 days a week, mon-fri 9-5 (far more common)
AA1 morning greeting used during normal days, time profile set 12am-11:59pm
AA1 out of hours greeting used when hitting night button
More auto attendants used to get more messages then just simple day/night