When your bags need to be up front depends on whether you are using Resort Airline Check-In or not. If you are flying on one of the participating airlines and want to use the RAC desk then you all must appear at the RAC desk between the hours of 5am and 1pm with your bags, but no later than 3 hours before your flight.
Your DME bus pickup will be between 2:45 - 3:15 before your flight.
Instead of hauling the luggage up front yourselves, why not have bell services come get it?? If you are staying in a cabin, just call them from your cabin. If you are tent camping, just go to a comfort station and call.
If they are just storing your luggage and you are not using RAC, then you don't even have to drive up that way with them, just turn in the golf cart at the Bike Barn and enjoy the last bit of time you have at WDW.