Corvette's mid-engined contender, which will make its race debut in this month's Rolex 24, made its first public test appearance in last week's three-day Roar test.
During Sunday's 15-minute qualifying session, which determined the pit stall and garage allocations for the IMSA WeatherTech SportsCar Championship curtain-raiser, Milner set the third-fastest time in the GTLM class at the wheel of the #4 car.
His time of 1m42.793s was only 0.108s shy of the class benchmark established by Daniel Serra in the Risi Competizione Ferrari 488 GTE.
"We have obviously done a lot of testing in private and felt like we came here with a good car," said Milner, who will share the #4 Corvette with Oliver Gavin and Marcel Fassler. "Certainly we have had a program to work through, but we had work to do once we got here with setup and things like that.
"I think we were a little bit out of the window to start with here in figuring the tires out, and the car setup wise and things like that. Each day that has gone by we have gotten the car a little bit better for each of us to drive and a little bit faster.
"It was a lot of fun there to drive in qualifying. Obviously just the fact that it is called a qualifying session you can tell that everybody ramps it up a little bit.
"Most of all just really happy with how the Corvette felt. All the changes that we have made the last few days have made a big improvement. It's encouraging that we can start with a balance that we are all not too happy with and find a good place for all of us.
"It was fun to have that qualifying session where we can go on low fuel and new tires and see how we good we could do. Third is pretty good.
"It looks like everyone is pretty close out there on lap times. It should be another very close and competitive for GTLM class at the Rolex 24."
#3 Corvette Racing Corvette C8.R: Antonio Garcia, Jordan Taylor, Nicky Catsburg