On the eight trips we've made to BWV, we have never been let in to our room early when we arrived on a Sunday. This is the day that most DVCer's like to check in and it seems to put a load on the housekeeping staff to get rooms ready. On the days we have checked in other than Sunday, our room has been ready when we arrived (usually around noon).
While this won't always happen, it's probably a good bet that your won't be able to check in early. We always pack a separate bag with swimsuits, suntan lotion, snacks, etc. to have by the pool if we don't have other plans.
Good Luck.