I doubt it requires anywhere near 10 dynos, normally I just run 1, and I suspect 2 or 3 dynos would work fine today... but since 10 dynos only costs 45 cents per hour, and it's presumably just for an hour or two, I simply threw two handfuls at the problem and went back to my actual work. Handling a one-time spike didn't seem like something worth optimizing when I could throw the price of a cup of coffee at the problem.