When does a Service Level Agreement (SLA) start and stop?
SLAs, All Supported Versions
SLAs end at 12:00 am PST on the day of the expiration.
For example, if your interface has configuration setting TZ_INTERFACE set to EST then your SLAs will expire at 3:00 am on the day of the expiration.
If you have a contact with an SLA that expires on December 31 and the SLA does not start until January 1, then there would be 24 hours where that contact would not be associated to the SLA because the SLA expires on December 31 at 12:00 am and the new SLA does not start until January 1 at 12:00 am.
Some potential issues during the time between December 31 and January 1 might be that the contact would not be able to perform any actions required by an SLA, such as viewing privileged answers or creating incidents.
For information on the timezone setting, refer to Answer ID 605: Setting the time zone in Oracle Service Cloud.