You can now add priority for each availability rule in Appointments plugin. You can override rules on any level from any level so there is no more hassles with availability definitions for staff or globally for all products. You can define rules that will override all of them.
Availability Rule Priority
Rules with lower priority numbers will override rules with a higher priority (e.g. 9 overrides 10 ). By using priority numbers you can execute rules in different orders for all three levels: Global, Product and Staff rules. This means that you can override rules defined on Product level by defining another rule on Global level with priority lower than 10, which is default.