When the sun does not set until so late, how does one observe shabbat? When does one light candles and when does one consider shabbat to be over?

The Tiferet Yisrael who was the rabbi of Gdansk (Danzig), refers to the question at the beginning of his explanation to the Mishna (at the end of Berachot Perek 1). The problem becomes acute in a place where part of the year the sun never sets or never rises. Contact Rabbi Meir Horden of Stockholm who can inform you of the exact times of shabbat in Sweden.