It's a tie-in to the series so more relevant than any other Clone Wars novels, and is still canon. It either reffered to the movie or Duel of the Droids, IIRC. Again, I don't think they'd jump around in the timeline that much. The episodes are out of order, yes, but there are no massive leaps forward as far as we know. If the Season 2 finale is in 19 BBY and Season 3 starts in 22 or 21 BBY...meh.