I have just purchased a new set of F) DL with ceramic bearing hubs and they are quite stiff.
When I spin the wheel upside down on the bike it quickly stops and there is no roll back to the heaviest point.
I own 30 wheelsets and this is my first wheelset with ceramic hubs.
The preload is correctly set up.
Is this noraml and do they need a few thousand kms to loosen up?
My Eurrus wheels bought a few months ago feel way smoother in the hubs and they are standard bearings!!

Mine never did that. They should be like butter out of the box!
Did you purchase from a reputable person/place?
If not, I wonder if someone switched bearings on you.

Take the front wheel out, and see how easy it is to turn the hub; it should be very smooth. Give it a week or so of hard riding; as far as I remember the wheels use the same Campy USB bearing as the Shamals, they might have some grease that needs riding in. Formula I bearings say the same thing on their website, that initially there is no noticable difference in rolling smoothness, but with time they come into their own and they are like glass; a wheel spin comparison with full ceramic, verses hybrid ( yours) and my Elites ( which remain a bit sluggardly after 2.5k) on youtube had the full ceramic outlasting both by 2-3 spins, and they were Formula 1.

If say 1k km's fails, then take them to a reputable bike shop that does shamals and maybe even yours, and ask them to look at the bearings and ask if they are the same as in the Campy Shamals or a shop version of yours.