Wikipedia
The Julotta is a Swedish service that celebrates the time of birth of Jesus Christ. Jul means Christmas, otta is the time which is slightly before dawn. The service is held every 25 December early on Christmas morning; at 7 AM in most churches, but in some churches it is celebrated at 10 AM, or as early as 4 AM. During previous decades, most Julottas were held at 4 AM. Traditionally, the service should end before, or at the time of, dawn: hence the word otta is the time just before dawn. Historically clergy was obliged not only to say the high mass but also mattins (ottesång) and evensong (aftonsång); today only the ottesång of Christmas remain but has been liturgically changed since and can now be the main service of Christmas Day, wherefore many parishes have no mid-morning high mass on Christmas Day.
It was the most popular service in the earlier days but now the Midnight Mass on 24 December has become more popular. People who hardly visited the church regularly in the rest of the year often visited the Julotta but they tend to go to the Midnight Mass or the service of Advent Sunday.