I had this Idea yesterday when I couldn't fall asleep. First I need to define the problem or rather explain what aspect of that question I want look at.
The scenario is I am on a navy map where I build up my base end eventually decide to build a navy factory and build a frigate which I send towards my enemy. I have an income of lets say 58 mass/per second so the factory and the frigate take up 10 seconds of my mass income. That frigate is now going to the enemy base killing some engies trying to build a navy factory. The frigate takes 100 seconds to reach the enemy base. So the question how much mass worth in engies would that frigate actually need to kill to be worth it? Here I am going to only look at economy damage and also ignore reclaim. (You can add that if you want to but it doesn't really change the concept I am going for). Also I am ignoring potential navy locking and the following additional costs my opponent would need to get back into the pond.
So lets say my opponent has the same income as me when I am building that frigate (58). If he is just ecowhoring for the next 100s. Also I will not bother with the exponential scaling of his economy and extrapolate his income linearly (minimum estimate). So 58 m/s100= 5800. That is about 6 t2 mex. So by the time my frigate arrives he would have 58m/s+46m/s=82m/s.
Now my model is that I would need to set him back more than 10s of his mass income to make the investment worthwile. That would mean the frigate would need to kill 820 mass to set him back more than it set me back. You could also call it pay for itself.
This example was an attempt of quantifying the negative travel time impact of any unit going on a raid.