Is there a way to block of certain times without changing your default availability or adding an additional availablity?

At the moment, no. However there is work going on to create Date Overrides feature that @Emrysal is working on, and it's almost done. So, you should be able to do this very soon. 🙂

@Ali found this information about the Date overrides feature release! Can't wait! We really need it! thank you so much!!!

@Emrysal is a champ 🙂