How long does the 'List Employees' API take to reflect changes made on the dashboard?

I terminated an employee and set their termination date to the previous day, making this change at 12:30 PM. Since then, I’ve been using the updated_since filter to fetch the updated employee list every 15 minutes. However, even though I terminated the employee at 12:30 PM, the API still returns this employee as updated at 1:15 PM. This doesn't seem correct because no further changes were made after 12:30 PM, so there shouldn’t be any new updates for this employee.

Could you clarify why this is happening? if it takes time then how much time will it take to reflect.