I'm not sure as the law is not yet precise and will be applied this winter for the first time. Depending on how it goes, it's application might be sligtly different.
The law says one should be equiped with winter tires from dec. 15th to march 15th.
A dispensation may become effective for 7 days if you want to drive south for example.

Tee law was already effective last winter but for rental cars only and IMO this was a GREAT thing. People who rent cars are not necessarily confident on snow driving.