Jusqu'à combien de semaines Midsummer Eve - NO?

Midsummer, also known as St John's Day, or Litha, is the period of time centred upon the summer solstice, and more specifically the Northern European celebrations that accompany the actual solstice or take place on a day between June 19 and June 25 and the preceding evening. The exact dates vary between different cultures. See wikipedia for more details.