"It's been hard work for Vanessa in the past five years," McCullum acknowledged. "She's spent a lot of it pregnant and has had to do it on her own most of the time. It's time for me to start investing time in my family and being there for dinners and helping the boys with their homework.
"I'm looking forward to it."
McCullum will miss matching wills with the world's most aggressive, highly skilled batsmen but says after meeting with coach Mike Hesson and manager Mike Sandle, he is comfortable sharing playing time this season with a younger crop of spinners, like left-armers Mitchell Santner and Anton Devcich, and leggie Ish Sodhi.
"We've got to get these guys up to speed and I'm looking forward to playing a mentoring role there."
McCullum made his T20 debut in 2007 as a 27-year-old with seven years of first-class cricket behind him. He made his ODI debut two years later and has racked up 61 and 84 matches in each discipline respectively.
His task has been one of the more thankless in modern cricket: to stem the flow of runs in the middle - and occasionally death - overs of short-form cricket. In these days of big bats, small grounds and murderous intent, an economy rate of five in ODIs and a tick under seven in T20Is testifies to his effectiveness.
Ally to that his ability to score quick runs in the lower order - he scored four half centuries in ODIs and maintained a highly respectable 20+ average - and field like a tiger, and it was easy to see how he became an invaluable part of New Zealand's limited overs equation.
McCullum was never a prolific wicket-taker and his 136 first-class wickets have come at a cost of 40 each, so he was never a compelling candidate for a test cap. In many respects, that gave him a clarity about his role and he could concentrate on his limited-overs skills.
As for particular career highlights, McCullum said any time he got to pull on the uniform and sing the national anthem was a special memory, but he did single out the quarter-final win over South Africa at the 2011 World Cup, played at Dhaka.
The Black Caps were defending a relatively paltry 221, but McCullum took the new ball and his 3-24 was central to New Zealand's 49-run victory.
"To come back and win a match we shouldn't have won was pretty special."
He doesn't have any particular regrets, though acknowledges that once he matured as a person he became a much better cricketer.
He'll admit it's been "cool" to play cricket under the captaincy of brother, Brendon.
"Every now and then it's hard case when your little brother is barking orders at you... but he deserves everything he gets in terms of praise. He's worked his butt of and created this team along with Hess and Mike Sandle."
Nathan, too, has worked his butt off to carve a niche for himself in the world of limited overs cricket, now he'll spend the next six months sharing that knowledge gained.
Then, as a less transient presence at home, he'll learn another form of working his butt off while trying to keep three boisterous young boys happy and in check.
