Another Rinterpto/Timeline question for an idiot

Ok good to know that this is the approach that i should be focusing on. I have that implemented, but i was having a hard time dynamically setting the length of the animation. (I know the time of animation, but i know it in a “dynamic/query’d from scene” sort of way). Set Timeline Length just sets how much of the curve gets played, it doesn’t adjust the length of the curve at all.

Am i missing something? If i have my target duration (say 2.2), and my curve length (1) Should i be using set playrate as 1/2.2?