Left Marrakech at midday, got to Tanger at 16:45 .... with a 45 minute fuel and burger stop. So only 4 hrs riding time Tanger to Marrakech ... on 90 odd mph the whole way on the motorway ... and guessing you add 45 mins to an hour for Ceuta ... cause some new branch of the motorway seems to go pretty damn close to Ceuta.
Its boring that way, but we had some administrative delays in Marrakech and had to leave as late as possible ... and had to make a 18:30 boat in Tanger .. which was made very easily as it turns out even leaving Marrakech at midday.
As others have said, watch for traffic lights and radar cops in abundance at the 20km non-motorway section near Rabat.
If you are gunning it on the big bikes I am guessing it will take you less than an hour to Tanger, 2 hours Tanger to Rabat, 40 mins Rabat to Casablanca, and about 1hr 40mins Casablanca to Marrakech. ... its not long at all on the motorway. If you took a 7am boat, and cleared the border quickly, bearing in mind you make an hour back, you could be in Marrakech for lunch if you gunned it with just one short fuel stop ...... but really not sure thats what you should be aiming for, unless you have a early deadline in Marrakech