Hi TheMart,
I just tried this on my project and it worked:
This is only the hiding part, not the reappearing part, but if you understand it then you can figure out the rest yourself.
Basically I check if the platform is not moving, if it isn't then I add to a variable I called TimeElapsed. I add dt - which is a variable that stands for delta time - the time that elapsed since the last frame.
Then I check if TimeElapsed is already larger than 3, and if it is I remove 10% of opacity from the previous opacity value (of the animation object, not of the collision object - depends if you have these in two different objects or not).
Let me know if that helped.