Not really. It could be they have massive traffic during US daytime hours, which is not evenly matched by traffic from the rest of the world during US night times, so they'll just run this batch during US night time and hence the 24 hour period.
If they're running their own DC (or their own hardware in a colo) then I believe the only scaling down can by shutting down the systems at night, which, while non-trivial amount in electricity savings, is not really much when compared to the total hardware CapEx or even the total OpEx.
And, even then, you have to consider the cost of shutting down and bringing them up and the complexity it brings.
Now, if they're using a cloud provider they can theoretically terminate the instances. But, even in that case, to do that, they'll have to use on-demand instances rather than use reserved instances which will probably wipe out all the savings.