TomUK:
That's an interesting take on the expression, and it's probably accurate, given the nationality of the author.
But here in the U.S., "calling time" has a slightly different meaning stemming from the world of sports. In baseball, if the team's manager (the equivalent of a head coach in basketball, football, etc.) calls time, it means he's requesting that the umpire (referee) temporarily stop the game from proceeding.
A manager often calls time because he wants to have a conference with his team's pitcher or replace the pitcher. Since the rules don't allow the manager to walk into the field of play while the game is in progress, he "calls time" (a request that's routinely granted by the umpire) and then strolls to the pitcher's mound, usually to either give the pitcher advice, check on the player's fatigue level or to simply wave his hand and call in a replacement pitcher.
It's similar to the expression "calling time out," which is associated with basketball, football and other sports.
Just thought I'd give you a perspective on what "calling time" means on this side of the pond.
(And as my screen name suggests, I'm not a teacher.)