Law / Notice period Poland (job termination) - does 'one month' equal to four weeks? [13]

[Moved from]: When exactly the period notice (when leaving a job) is changed from 1 month to 3 months - Poland

Hello!
I know that after 3 years working for the same company, the period notices changes from 1 month to 3 months. However I am not sure when exactly this change happens.

If, for instance, I started to work for a company on the 10th of May, 2016, if on the 9th of May 2019 I communicate that I am leaving, what period notice will be applied, 1 month or 3 months?

The point is that when I communicate it (in such example) not 3 years have passed yet, but more than 3 years will have passed if we take into account the day I leave, not the day I communicate that I leave.

Thank you in advance.
Regards