Fixed lease dates are a legacy of 18th-century Quebec, when it was a French colony. Mr. Warren said that Quebec simply followed French laws of the time, which set May 1 as the beginning date for all legal agreements, including leases.

Forgotten in France, the May 1 lease law persisted in Quebec until the 1970s. It was unpopular in its own way. Carole Rondeau, who was helping her two nieces move about half a mile on Monday, recalled that her classmates would suddenly disappear from school when she was growing up as their families moved out of her neighborhood.

In 1973, a new law ended any required lease date and extended all leases until July 1, 1974, in a bid to end the disruption to the school year.

But Mr. Warren said July 1, against all obvious logic, has persisted as Moving Day. French-speaking Quebecers, he said, move far more frequently than most Canadians, but they generally do not stray beyond their neighborhood. Some move from one side of the street to the other, and it is just more convenient to make such apartment swaps all on the same day.

“They are constantly on the move, but they don’t go anywhere,” he said.

The inconveniences are many. Montreal, where 62.1 percent of the population rents, has unique disadvantages for movers aside from the many narrow streets. In a bid to increase apartments’ floor space, there are few staircases inside buildings, and the steps are cramped and winding and open to the elements. And unlike apartments in the rest of Canada, the ones here rarely come with kitchen appliances, adding to the movers’ burdens.

Moving companies and truck rental firms cannot meet all the demands of Moving Day. Robert Lalonde, the vice president for Quebec of Discount, a rental firm, said his company doubled its rates on Monday and was expected to rent out each of its 1,000 trucks at least three times. Tom Filgiano, the president of Meldrum the Mover, said potential customers will start calling his office later this week about Moving Day 2014, although he will not accept bookings until next spring. “We would love to be like the rest of North America,” he said somewhat wistfully.