Items moved through the ice in some glaciers faster than in others, so a body moving through the ice at Fox Glacier would likely only take one or two decades to emerge, he said.
Tasman Glacier might move an item through the ice over several hundred years.
Mackintosh said crevasses, on the other hand, usually opened up for a few years at a time and then closed, so he did not believe the body would have been there for 30 years or more.
"If a body turns up in a crevasse, my guess would be that it's actually relatively recent," he said.
"My gut feeling would be that it's just sort of been in the last five years."
If that was the case, he said the body was likely fairly decomposed. The person probably fell into the crevasse, he said.
Police may have to wait until Monday to retrieve the body because of the weather.
The police operation to examine and recover the human remains was yesterday postponed for the day after clouds closed in, Sergeant Mathew Tailby said.
"Police travelled to Fox to undertake the recovery, however the deterioration in weather conditions has made it unsafe to fly to the glacier.
"We will now continue to reassess the weather over the next few days, but it is not believed conditions will be suitable to access the Glacier site before Monday.
"Once we can get to the scene a post mortem will be required to identify the remains as they have been there for some time.
"Once identified, police's first priority will be notifying their next of kin."
Human remains expert John Dennison said the body could be in any condition, from perfectly preserved to deformed from the pressure of the ice.
Dennison once examined a single bone discovered at Fox Glacier, and said although the bone could have been there for up to 10 years, he was able to find residual hair and tissue on it and determine the bone was from a young, fair-haired male.
Dennison said investigators would need to cast "a very wide net" to discover when the body originally went missing, "and then narrow it down from there".
The ice and any lack of oxygen could preserve the body "in the state in which it had gone down there, but the body also might not have been preserved". Without more information it was too hard to tell what state the remains would be in, he said.
- Additional reporting by Greymouth Star