Guitarhacker:

ri·tar·dan·do
/ˌrētärˈdändō,ˌritäːˈdandəo͝o/
Music
adverb
(especially as a direction) with a gradual decrease of speed.)

I disagree about "In my experience, it happens over a 2 measure (not 6 to 8) range".
In the song I'm doing, I need the "slow down" (not fade out), over 4 bars, but I have used mored bars in other songs.
What I'm after is a function similar to the one in the F5 Bar Settings window, where you click on the down arrow by the All Instruments setting,
and instead of selecting "Fade per bar", have a selection that does "Ritard per bar".

Of course the heading under "Instrument Changes at This Bar" may need to be changed from "Volume Changes" to just "Changes".

Thanks!
LLOYD S