All that remains for leaderboard optimization isn't really outside the spirit of the game:
(Why yes, since you took my "1" away from me I have instead claimed the perfectly optimal solution.)
Could be amusing to write a script that took a correct solution and optimized it with a binary search of the elapsed time between packets firing.
Also an interesting thing about ordering with regards to collisions with a single cell in the grid. Note that both of the first two fire "simultaneously," would reach the same node simultaneously, and yet the "second" one passes through. I would call that correct, it's just interesting.