@kezo KIA are apparently strict on services being done on time (as well as genuine parts). My car as gone past its service due date.
As Hyundai, so would expect the same for Kia, you are allowed one month or 1,000 miles after the due date. Most manufacturers use long life 2 year serviving, not sure with Hyundai/Kia, as it’s always been 12 months.