How to calculate how long an iTween will take

I'm using a speed based iTween (MoveBy) that animates my object X distance by S speed. Anyone have any ideas on how to figure out the length of time this animation will take before it is run? I'm basically trying to have something happen at the middle point of the iTween animation.

I know that there is a Time based iTween, but I can't use it because the distance is always different for each object and I wouldn't want objects travelling a short distance doing so in the same amount of time as an object going a long distance.

give same time for each path for long path it move faster than the shorter one .........

if u wanna move till a long path's middle node.get the node and represent its index