Maintaining and Exposing one centralized calendar module across systems under Collaboration

As part of OIC/OPA the Systems/Application which are getting integrated or involved in the process sometimes need a centralized Business calendar(Working days configured specific working hours possibly with holidays and leaves). As of now we have calendar accessible only within OPA and it imposes systems which are collaborating together to maintain individual calendar causing lot of sync issues and lacks in accuracy.

 We recently wanted to implement a use case where SLA Duration like Violation period has to be maintained and validated in every stage/milestone of the workflow by different application but end up in maintaining individual Calendar and SLA calculation lead to different decision in edge cases.