NSDate(AWS) Category Reference
Set the clock skew for the current device. This clock skew will be used for calculating signatures to AWS signatures and for parsing/converting date values from responses.
the skew (in seconds) for this device. If the clock on the device is fast, pass positive skew to correct. If the clock on the device is slow, pass negative skew to correct.
Get the clock skew for the current device.
the skew (in seconds) currently set for this device. Positive clock skew implies the device is fast, negative implies the device is slow.