I have a string of about 8 Xmas lights that run off two C batteries. The string is 4' long, and weighs about 1/4 pound. I plan to launch a tethered (30') balloon before the 25th. I plan to turn on the lights at6 pm and off at 10 pm. Presently, I would need to pull the balloon down and disengage the power. Maybe there's some simple timer I could use. I'll probably use two AA batteries instead of the C batteries to reduce the weight. Two C batteries weigh about 2/3 pound.
My balloon will probably be a 10-15 gallon garbage bag filled with helium.