We have checked in around 9AM, the room wasn't ready but we just went on our way and the room was ready when we got back to the resort. We also checked into VWL once around 11AM and the room was ready.
Don't worry, hit the parks. Just as Bobbi said, if your rooms not ready they will store your luggage and you can be on your way. You may want to keep your swim suit handy (in a carry on, purse, gym bag) and then your off.
Have fun & Float the lazy river for me