Your requests can be broken into two separate components - there's the 'do something' part - start a playlist; stop a playlist, etc. - and a scheduling component.
The 'do something' here is pretty trivial and could look as simple as:
tell application "iTunes"
play playlist "90’s Music"
end tell
Just substitute the name of the playlist you want to play.
The trickier part is the scheduling - getting it to run at the set time. There is nothing built-in to AppleScript to do this.
You have two basic options - simple and complex.
The simple options is to use some other application to trigger the script. An obvious choice here would be Calendar.app which has the ability to run an AppleScript for any given event on the calendar. Just create a repeating event at 7am every weekday and link your morning 'Play' AppleScript, and another event at 7pm every day to your evening AppleScript.
That's the simple thing, although it doesn't meet your 'auto-restart' condition - if the power goes out, nothing would happen until the next calendar event (either 7pm or 7am, as appropriate).
A slightly more complex implementation could be setup to run at startup and stay alive in the background, periodically checking the time to work out what playlist should be active. Like:
use AppleScriptversion "2.4" -- Yosemite (10.10) or later
use scripting additions
property dayList : "Daytime Music"
property nightList : "Evening Tunes"
on idle {}
my doIt()
-- check again on the hour:
return (3600 - ((get time of (get current date)) mod 3600))
end idle
on getCurrentPlaylist()
-- assume it's evening/weekend
set currentPlaylist to nightList
set curTime to (get current date)
set hr to (time of curTime) div hours
if hr ≥ 7 and hr < 19 then
if (weekday of curTime as integer) - 1 ≤ 5 then
set currentPlaylist to dayList
end if
end if
return currentPlaylist
end getCurrentPlaylist
on run
my doIt()
end run
on doIt()
set pl to my getCurrentPlaylist()
tell application "iTunes"
playplaylistpl
end tell
end doIt
As you can see, this is much more complex, although 90% of the code is in working out the current date/time and establishing which playlist is the right one. The good thing about this is that if you save it as a Stay Open application and add it to your login items, it will run as soon as you log in (which, of course, requires automatic login for your account, which is a whole other issue 😉 )