Hello and thanks for taking the time for a review. It is not obvious at first but more than 3 Availabilities can simply be added by adding a second Set Availability element on the page. Please contact us if you would like more details into exact details into how to do this.
We default to just 3 inputs in the one element to keep unnecessary bloat out of the plugin element and keep the plugin simple for the majority of use cases. (plugin author)