FPS Question

I was wondering if it is possible to set the FPS diffrently to each layer.. or do i have to have it the same threw out the whole animation?

for example

i want two people talking, (text, not voice) and i dont want to set the FPS to fast or too slow, b.c later let say something that will happen iw ant it to go fast.. so is it possible to set two diffrent speeds at all as it is going threw a new frame or anything like that?