You should have a Rental Voucher from the owner with your dates of stay--make sure you copy one per car (mandated as of May 1, 2009) and you just take this to the Clubhouse and pay your $10 refundable deposit per person and could use the facilities. You can change in the restroom and I believe there is also a shower room in there. You could arrive as early as you want in the day as long as the dates are on your rental voucher and feel free to use the facilities in the Resort and at the Clubhouse. The owner may allow you early check-in if no one is checking out the same day, sometimes you won't be able to be guaranteed until upon the rental time in case of last minute rentals.
Sandy