For those in the US, though, please do call your representatives.
* It's clearly going to take more than a day to achieve a positive outcome in a system that was established over many decades
* What happens when "the day" ends?
* Since the action is framed as "the day", this is how the media will report on it - including outcomes of the day. These outcomes, whatever they are, will be packaged with the day and thus more easily dismissed than, say, "the movement" (which continues to grow) or "the tide" (that is turning) or "the big cleanup" (which must be repeated regularly)
If something like this took place once a year (where sites protest mass surveillance) it would assure that people continue to discuss the issue instead of slowly forgetting about it.
Labeling the effort "The Day We Fight Back" has a certain "shock" value that intrigues people. If instead it were marketed as "let's talk about long-term strategies for dismantling mass-surveillance" support would probably trickle in.
After all, signing a petition or putting a url on your site isn't really "fighting back," it's a protesting.
Getting out a message means bringing as many voices together at the same time. Getting press coverage. Making noise.
Diluting that influence over a longer period of time dilutes the call.
That said: yes, a longer-term call to action would be a damned good thing.