June 25 is the date of Midsummer Night.
According to Wikipedia, the celebration of this date in Great Britain goes back to the 1200s and continued through the ages (with some exceptions) in various forms.
The date is also significant in Great Britain because it is one of four “quarter days” traditionally marked in the country throughout the year when certain financial or labor duties were realized. The other quarter days include Lady Day (March 25), Michaelmas (September 29), and Christmas (December 25). You’ll notice the religious correlation of these days being the Christian Feast of the Annunciation, the Feast of St. Michael, and the birth of Christ. Midsummer Night itself coincides with the Feast of St. John the Baptist.