A lot of entries have had months/years of work-in-progress (or even use assets that have been made long-before but never used before) and are being entered for the contest. This is within the rules of the contest, so it's normal to see this. Obviously, it's hard to compete against those maps, but that's just the challenge I guess most people make a map for a long time, and then wait for a good contest to enter it.
Even then, working on a map regardless of when you started it, can always be useful for later. In fact, if I'm not wrong there was once a CEVO contest or some other one of the same level, where one of the losing maps was accepted by Valve regardless, which I guess is the biggest reward you can ever have. In any event, whoever thinks any of the entry maps looking extremely good (or a very detailed greybox that looks insane for just a month's time of making) have been made only from the announcement date of this contest, is kidding himself. So yes, start crunching those mapping skills !