In your PLC program, setup a GSV with WallClockTime as the class, LocalDateTime as the attribute and a tag that is an array of 7 DINT's. This will store the PLC time in the array, [0] being the year, all the way up to microseconds in [6]
In FactoryTalk, go to Global Connections and put your new array in the "Remote" fields. And if I'm not mistaken, you put a tag in "Remote Date and Time", when that is a 1, it will sync the time.