I just replaced the rear pads & rotors on my G6 GT yesterday. I used a 1/2" wrench to turn the brake piston in. Took about a couple minutes to do for each side. I would do a full turn pushing with light pressure, then I waited half a minute, gave it another turn, another half minute and another turn put it all the way back in place.
It's also good practice to pop the hood and remove the brake reservoir cap to relieve any pressure.
'11 Ram SXT 4x4 quad cab - 5.7L V8; 128,200kms
'09 Malibu 2Lt 3.6L - 140,000kms purchased 1 March 2019
'06 Pontiac G6 GT - 3.5L V6; 162,000kms (rear ended 15 Feb 2019, and given totalled title by insurance)