Kelly has always been a top runner. In games the Sandringham Dragons midfielder strides from one end of the ground to the other and rarely looks bothered. But he hadn't done a race of this length before, so had no benchmark in mind. There was another factor, too.
As a player eligible to be selected in last year's mini-draft, Kelly was a year younger than everybody he was running against, many players who had done this before, who were seven weeks off joining clubs and starting AFL careers.
None of that mattered. Kelly ran the six-and-a-bit laps of Etihad Stadium in nine minutes and 48 seconds, recording a time better than anyone at the combine.
Only three others in the history of the AFL's testing had gone quicker. The mounted Sherrin he won as a prize for the effort now sits proudly in his family's loungeroom.
"His football ability had been obvious throughout the year. That ability to make great decisions, use the ball well, be courageous. He looked a real footballer," says Kevin Sheehan, the AFL's national talent manager.
"But what we saw at the time-trial was a superb first-choice athlete. He moved like a beautiful runner…had the bounce, acceleration and then the ability to stick and keep going at that speed. I hadn't seen that aspect of him before. It probably explains why he gets so much footy."
It finished a year where Kelly did everything right.
As a bottom-ager he played four impressive games for Vic Metro in the NAB AFL Under-18 Championships. He stood out in a few of the Dragons' games in their push to the TAC Cup preliminary final, and stuck at his task for school side Brighton Grammar. His results at the combine only enhanced his standing.
But he still didn't get picked in last year's mini-draft, with Gold Coast snapping up Jack Martin and Melbourne giving a lot to add key forward Jesse Hogan to its list. Three hopefuls could not fit into two spots, and Kelly missed out. But he didn't waste the opportunity.
"It was huge for me," Kelly told AFL.com.au.
"I was just there for the experience and I think it's made me better this year in watching how the players go about it. I've been able to work on personal things in the pre-season from what I saw last year."
Kelly started to meet clubs towards the end of last season. They made no guarantees on their plans for the mini-draft, where they could trade with the Giants for access to players who were eligible for the 2013 draft, but as it got closer Kelly found himself wanting it more.
"I definitely did want to get picked up, but I wasn't expecting anything," he said. "They totally deserved it."
He watched Hogan and Martin make their NAB Cup debuts and was happy for his former AIS-AFL Academy teammates, but didn't find himself thinking he was close to being in their shoes. Instead, he has turned his attention to being picked at the end of this year.
Kelly is competitive beneath the surface. It's one reason why recruiters who talk about this year's draft mention his name as part of the standout group.
The other reasons are obvious: he's a beautiful left-foot kick, for a wiry frame he stands in the way of traffic, and he has the things that can't be taught, like composure, poise and awareness.
The quiet determination has always been there, even at home.
Josh's dad, Phil Kelly, won two Sandover Medals in Western Australia before moving to Melbourne, where he played 61 games for North Melbourne in the 1980s before hamstring injuries ended his VFL career.
The endurance comes from Phil, who ran a 2.05-minute 800-metre race when he was 15. Josh made it his goal to eclipse his dad's time, and it didn't take long.
"I ended up getting him," Josh says. "I did a 1.56. It was a bit of a personal best that day." (It was also a record time for his school.)
He's also making sure he's ready for everything that's thrown at him this season. Over summer Kelly engaged a sprinting coach to make sure he could add a burst of speed to his endurance base.
It's not a surprise he has thought about his game and identified areas he wants to get better. In meetings Kelly listens, takes things in, and jots down notes. After every game, and most training sessions, he whacks on his muscle compression pants and jumps in the ice bath so he's ready to go for the next day.
His outlook on this year is clear.
"It's just a totally clean slate. It doesn't matter what I've done in my footy so far last year. This year is totally new. You've got to start again, you've got to build up the way you play and you've got to get reselected in teams. There's no guarantees this year," he says.
"I want to keep improving. I'm not complacent with how I played last year and how I went for Dragons, Metro and for my school team. I just want to keep improving everywhere I play footy."
Follow AFL website reporter Callum Twomey on Twitter at @AFL_CalTwomey.
This is the first of AFL.com.au's 'Prime Prospects' series which will feature throughout the season on the road to the NAB AFL Draft.n
