Events started today at the 2018 PyeongChang Winter Olympics, 1 day before the Opening Ceremony. This is not uncommon, and also occurred at Sochi in 2014.
Of the 23 Winter Olympics to date, including PC, 14 of them started on the day of, or after, the Opening Ceremony, and finished before or on the day of the Closing Ceremony. This happened consecutively from 1988-2010.
The first Winter Olympics at Chamonix in 1924 had its sporting events end the day before the Closing Ceremony, the only time that has happened.
In 1932, the events finished 2 days after the Closing Ceremony, because weather had caused postponement of events.
In 1964, 1968, and 1984, the events started 2 days before the Opening Ceremony. The events have started the day before the Opening Ceremony in 1976, 1980, 2014, and 2018.