Don't know for sure if it's normal but mine does the same thing. Seems to take about 1-2 minutes before clutch fan fully disengages. I say fully because it's still somewhat engaged all the time to move air across the other stuff in front of our engines.
Read in some magazine/shop manual/book (can't remember which) that the viscous fluid in the clutch fan settles to the bottom of the clutch fan housing and takes a minute or two to get re-distributed when re-starting the engine.
Have a great day
Tom G.