Just a wild guess, but looking at them, starting at image #1 then clicking through some of mine in sequential order, the numbers may/might/maybe have something to do with the numerical placement of the images on the pages. That would be my S.W.A.G. (Scientific Wild _ss Guess) ;)
It looks to me like a measure of how long it takes for the image to make it from FAA's servers to your screen. If you do a traceroute, you get a similar kind of thing, where the hops start taking a little longer and little longer until the packet makes it from the start of the route to the end of the route.