I'll try to explain.
If you set SLA to calendar hours then the time left would be a bit less than 14 days, since every minute of every day will be taken into account. It you choose to use business hours then only those hours will be taken into account. By my calculations your business hours are set around 8 hours a day 5/7. To come to this:
* Hours worked during one week: 8 * 5 = 40
* Days worked in one week: 40/24 = 1.7
* Amount of weeks needed for calculation: 14 / 1.7 = 8.2
* Total SLA days to be counted: 7 * 8.2 = 57.4