"His whole body clock biorhythms are going to go through some sort of revolution when he stops doing that."
Barnett will join the NZME team as a host at Newstalk ZB in early 2019. He said earlier he had done breakfast radio for 26 years and waking up at 4.30am was getting "less palatable''.
"I completely and utterly sympathise with him,'' Plunket said.
"So I think for his family and for his life, moving somewhere where the hours are more normal is just a fantastic move.
"He's also a really good broadcaster and I think he'll probably be even better once he's not so sleep-deprived."
Former broadcaster Sean Plunket. Photo / Dean Purcell.
Plunket, who now works as a freelance communications consultant, said it was possible listeners who had followed Barnett over the years would move with him.
He acknowledged that Christchurch listeners were particularly loyal - especially if Barnett would still be based in Canterbury.
"I guess that's up to the audience, but I wish him well because he's a hell of a nice fella."
Plunket had one bit of advice for his old mate: "Have a good break between jobs.''