5 year Belgian white card...how long can I stay away from Belgium

This is not the place to ask such a question.
If any answer that you get is wrong, you cannot say to the immigration officer, 'But that's what I was told on the xpats website.'

Any person leaving the country for more than 3 months must declare at the commune. The commune provides a document that allows you to stay out of Belgium for a maximum of 1 year but you must return to Belgium within 1 year to guarantee your current residence status...