Generally, once a thing is properly up at the DC digital and comixology sites and available for download, it is pretty much always available. I haven't seen them rotate stuff out, to my knowledge.
The thing that is unique about today and tomorrow is the price…all the books I mentioned are on sale for 99 cents an issue right now. I suspect they will go back to $1.99 on Saturday, but will still be available. Hope that helps!