Using custom properties

I’m having some array modifiers, and curve modifiers. and I want some cubes to grow. So they all vary a bit in length, from unborn , to finnished.

for eg. one is 2.5 when it’s done, and a other is 50.1, Now I really dont know how to go about this.

But can I add custom properties to them, min 0.0, max 1.0, and have this property drive the length, so they never can grow to long.

and when I animate it I animate the driver, just between 0.0, and 1.0(complete) for all.

or is it some other way to link or use this custom properties thing ? thankfull for answers.