I did it today as it was convenient and no long trips planned in next month.
In the past it has been mid Nov to mid/late Mar depending on the weather.
Always do it before the weather people talk about the first snowfall/freezing rain as suddenly the tires shops go from nearly empty to insanely busy.
NOTE to be eligible for (usually 5% insurance discount): a) it must be all 4 tires b)tires must have the 3 peaked mountain snowflake symbol, winter and all-weather tires have this but all seasons usually do not c)see below about dates
Dates: 1)"To qualify for the winter tire insurance discount, some insurance companies require that you have winter tires on your vehicle from
November 1 to April 1. Other companies state that your winter tires must be on from November 15. Date requirements vary. Some companies specify installation must be done by November 30 and still others set December 1 as the latest installation date."
2)"Quebec is the only province that legally requires every passenger vehicle to have winter tires
between December 1 and March 15"
If any other jurisdiction mandates it in Canada I think the Quebec dates are a reasonable minimum.