The traditional period of mourning is one year.
A year is a long time in todays fast moving society. Certainly some of the older generation of Pole will observe this but it's not as common now.
The younger Pole lives a different life so although mourning may go on inside, outwardly 'life goes on'. Of course, still the first anniversary of death is observed and may still be seen as 'officially' the end of mourning.