If they do not instantly shoot the drones down and seize the operator(s) the AF has already failed the tests. Same as the failed test with the stratospheric balloon.

What if the drones didn't loiter in the air for 4 hours, but rather "hopped", resting on the ground and powering down.

Powered optical spools or really cool batteries or power line recharging as other wildcard guesses.

...or a ton of drones redeployed at intervals.

That's all the guesses, y'all are going to have to scrounge for more. I'm going with the "hopping or bounding" guess.