In essence this thing is supposed to help you avoid forgetting when the bad vs. good times are to call someone... or to remember not to normally use some number you otherwise would. In other words, this tool helps users to be considerate -- a concept which the word blocking doesn't suggest.
If you stop calling it blocking then you don't need reverse -- some other word.
The confusing terminology did "make me look" but that's probably not a strong marketing strategy. Before I looked I couldn't imagine what in the heck "reverse blocking" was supposed to mean.
I'm afraid the name "call me not" has the same problem. I'm not sure what to suggest for a better one.
Feature-wise: seems like there could be a "social" / "groupware" kind of aspect to this. E.g., I can publish my schedule that might get abstracted down to "good times to call" for various groups of people, and the app can somehow just join those against my contacts list to automate .....
The "Call Me Not" app name I agree is confusing, but it sounded really catchy and a whole lot better than "Call You Not", so we stuck with it.
We did consider other groupware/google calendar approaches as well, but there was the question of implementation and the receivers' incentives to download the app and/or publish "don't call" times on their calendars. We ultimately decided on this approach for a first pass since it fit _my_ needs perfectly, at least. Completely changing the mechanics in later versions is not out of the question though, and will be based on valuable feedback we get from users like you =)
UPDATE: Title changed as per suggestion!
Also: "when to call" --- brilliant! perfect (imo).
