Amazon Time Sync Service now allows you to easily generate and compare timestamps from Amazon EC2 instances with ClockBound, an open source daemon and library. This information is valuable to determine order and consistency for events and transactions across EC2 instances, independent from the instances’ respective geographic locations. ClockBound calculates your Amazon EC2 instance’s clock error bound to measure its clock accuracy and allows you to check if a given timestamp is in the past or future with respect to your instance’s current clock. On every call, ClockBound simultaneously returns two pieces of information: the current time and the associated absolute error range. This means that the actual time of a ClockBound timestamp is within a set range.
Source:: Amazon AWS