Path constraint switching and timing I am working on my character animation project. 
I want to create multiple paths for my character to follow, (do action).
For Example, follow the first path from frame (x) and (do action) until the end of the path and SWITCH path instant/ delayed time and do another one.

I don't know what makes it so difficult but the Start/ End in F-curve Modifier doesn't work, is that i have wrong concept on the workflow or something else?
I recommend you for using bake animation. The follow step :


First, you set the object to follow the path by adding it on the "Add Object Constraint" 
Then, you set the thing, like control the speed (actually just control the frame), direction etc
Bake animation
The switch to another path using dope sheet.


How to bake steps you could check this link :
How can a path animation be used as an action in the game engine?

Hope this help :)