Meaning of Title?

Has anybody any insight into the title of this movie?

I thought it may have been reference to the length of time of their ordeal.

However... this movie appears to take place in summer since the characters are wandering about all night in normal (in some cases skimpy) clothing without being bothered by the cold. Also, a younger character is willingly left to sleep in the barn without a coat or bedding. This would not be realistic in England, except during an particularly warm summer spell.

In British summer time there are nowhere near 13 hours of darkness, let alone adding in the extra hours of darkness before 'things get going'. For there to be AT LEAST 13 hours of darkness the film would have to set between about late October and early April, which for me, doesn't fit with the whole "night party in the barn" scenario given the protagonists' attire.