Chrysler starter spin down time

It's a Chrysler trademark for sure.
Those starters have an overrunning clutch on them, to deal with engaging them with engine running.It's not a big deal, unless you did it every time for like 10 years.
Chrysler made those old starters in several flavors, and they are interchangeable. Be sure to get the six banger one.I believe it is rpm limited, by internal wiring.

The spin-down time is related to how fast it is spinning when you back-off the key. A high compression engine, or a cold engine might be spinning at a slower rpm than a tired or hot, slanty. Or if you fail to release the key in a timely manner. These are all factors.