Any decent synchronization system must not replace a file with a version with an older timestamp, must set timestamps on synchronized files to exactly the same

Any decent synchronization system must not replace a file with a version with an older timestamp, must set timestamps on synchronized files to exactly the same values as the timestamps on source file, and must replace the files atomically. As long as everyone follows these basic rules, and you only edit files on one system at once, it's going to be OK. (which is pretty obvious, btw)