Wishing your wife a lovely time caring for her little one.
And yes, Feb 24th, your son's birthday is a very good day to start that journey. I'm completely unbiased about that of course as it just happens to be my birthday too :)
$20K to pay off IS a lot, but small chunks between now and then should mean that you are very close to achieving your goal. I'd suggest putting ALL her wage from now until Feb into the repayments. After all, it would be a valuable experience before heading off into one income territory, as well as giving you the best base possible to do that from.