Forget the filter at sunrise at 6 am the sun won't be fully up, unless you want the sun in the photo, shoot with your back in direction of the sun. You have a 2.5° spot meter use it for metering the balloons, try to get the reading of the car (Balloon) or another part that aproximates 18% gray. Another possibility is to take a reading of objects that are higher and will be lit in the same way as the Balloons for example a treetop.
Good luck and have fun
Dominik