At this point the clock would have advanced by 102 seconds, effectively making up for the 2 seconds that it was behind. One could specify all the time sources and other arguments and check out if TimeSync gets any errors. The defaults for some arguments are different in each case. Thus, when testing time sources one can see the errors in the console and make changes accordingly. At determines when TimeSync starts synchronizing.
Period is the time duration from one synchronization point to the next.
If you reboot the machine TimeSync will start automatically. This will be half the period that was specified up to a max of 30 minutes. Naturally, TimeSync cannot do better than the time sources that you specify. If the time sources are not accurate your clocks will not be accurate either. Hence you need to find machines that have accurate clocks.