How to animate % along a path

Hi all,

Just playing around motion paths with cameras, I was wondering if i could create keys for the % value as i cant seem to get it to work.
I’m sure there is a way to do this
Example: At frame 30 it reaches 50% but then at frame 100 it reaches 100% effectively simulating speed

Any help would be greatly appreciated

https://knowledge.autodesk.com/support/3ds-max/troubleshooting/caas/sfdcarticles/sfdcarticles/How-to-animate-an-object-along-a-spline-using-Path-Constraint.html