I'm planning to go tomorrow, but I'm confused why they're doing it on the fourth. Nobody is going to be in the building we're gathering around. And lots of people are going to be out of town.
Mostly symbolic reasons (independence day, 4th of july, 4th amendment, etc), and it'll be nice because everybody will have off from work. There were some long, drawn out discussions early on in the planning phase from which it was agreed that July 4th would, in fact, be the best date on which to hold these protests.
I agree that the date was a poor choice. So many people traveling, barbecuing, and engaged in other activities. Despite this I will attend as well tomorrow. It'd be pretty cool to see Alexis Ohanian at the rally (I believe his is the comment currently (5:37PM) above yours).
Although pvnik who replied to you points out everyone being off work which is a very solid point. Apparently it was decided to be the best date. I guess I like the symbolism. Still not sure though.