You want it to be overt without being explicit, if it looked like an accident it wouldn't be threatening.
How would you blow up a pipeline without anyone noticing?
If there was a 1-month delay between the explosions, the people claiming it was coordinated would look a lot less credible. Particularly with the presence of large numbers of people with stakes in the outcome who will argue that the reality that makes them happiest is real.
If nobody notices, did you really blow up the pipeline?