Why does an incident's due date include the holiday we recently added?

Environment:

Oracle B2C Service, SLA

Issue: 

I have added a new holiday (World Day) but it is not selected on the SLA (Service Level Agreement) instance used for my organizations. 

Resolution:

When you create a Holiday, which you want to be used on the existing Service Level Agreements, you must edit the Response Requirements on each SLA instance to include that Holiday. For example, if you want the SLA to be suspended on World Day for Org1 there are two steps to be taken: 

1. Edit the SLA instance associated to Org1 and select World Day on that Response Requirement. Edit SLA
2. Then, in order for the new terms of the SLA to be applied to existing contact or organization records, steps will need to be taken to reassociate the records to the new version of the SLA. The steps to do so can be found in the following answer:   Answer 2820: Creating new SLAs rather than modifying existing ones

Related answer: