Schengen area covers 26 European states (including Poland and 21 other EU countries) which have abolished passport checks on their shared borders, also known as internal borders. At the external borders all the Schengen states apply the same solutions. The Schengen Borders Code lays down a common set of rules concerning the checks on people, conditions of entry and the duration of stay in the Schengen area.
One of the crucial principles for people travelling in the Schengen area (no matter if they do it under visa-free movement or based on a national or Schengen visa) is that their stay in the Schengen area cannot exceed 90 days in the last 180 days. It means that your passport needs to remain valid for at least 90 days after the entry into the Schengen area.
Regardless of the time of day of your entry into the Schengen area, the day of entry and the day of departure count as full days of stay. You can calculate the number of days of your duration in the Schengen area using the data from your visa and the calculator.