the method I came up with is https://youtu.be/CIGwQMIQH6M (the result after 00:54)
First, I mention my method also doesn't run smoothly, so I'm not sure it's helpful.
As the duration is changed, the offset ticks should be changed.
Set two curve data sources connected to the offset ticks of two curved vectors.
In your example, the duration number becomes 3/4, so do the same for the offset ticks.
the one 80 to 60, the other one 40 to 30.
Probably the gap is now quite small but when you try to slow down the speed, it is not a natural movement.
If you don't satisfy that result, you should find a new way. that may bring a better result.


