It's my understanding that the transportation is supposed to start 1 hour prior to the earliest scheduled (public) event. So if you have the Keys to the Kingdom tour at 8:30 even though the park isn't scheduled to open until 9, then the transportation should be running by 7:30. That said, however, many folks have stated that the buses start at 6:30, but that's from leaving their "Terminal" and not at the campground. Also, it's been suggested that if you are there present for the FIRST boat to MK you may still be at the back of the crowd for the Rope Drop (show). It has also been suggested that the boat from FW to Wilderness Lodge (and the Contemporary) actually is earlier and less crowded. You take that boat to the Contemporary, then walk to MK and you can get to RD early and near the front.
Your Mileage may differ and I have not tried this personally. I Know we have made RD several times from FW on the normal boat to MK, but we are usually in the back of the crowd. This is not really an issue for us, since the "Show" is UP at the train, you can basically see it well from anywhere inside the gate (where you scan your Magic Bands)