While resetting your DoTs too early is usually a damage loss on paper, it's worth noting how DoT ticks work so that we can understand some of the cases in which early application could be useful.

Ticks are not every three seconds of the DoT's duration, but at fixed server-wide intervals of three seconds at which all DoTs tick simultaneously regardless of their duration. If the first server tick happens one second into the DoT's duration, then the final server tick will happen two seconds before the DoT expires, and you could refresh the DoT during these two seconds at no loss.

Obviously, keeping track of the server ticks with any degree of accuracy would be too much to bother about for most people in most cases, but if one so desired, one could maximize damage output by taking advantage of these scenarios when they arise.