And you think the OP noticed that?

Yes. It sounds to me like he ran a series of tests that looked something like this:

edges       time
---------   -----
  500_000   1 min
1_000_000   2 min
1_500_000   4 min
[download]

And he recognized that as an exponential progression. In any case, there's no cause for making snide remarks about what he did or didn't notice.