on the eve of (something)
Immediately prior to something; just before something. Sometimes literally meaning "on the evening before (something)." Militants attacked the embassy on the eve of the anniversary of the historic peace agreement. She got cold feet on the eve of her wedding and got on a plane to Europe.
on the eve of something
Fig. just before something, possibly the evening before something. John decided to leave school on the eve of his graduation. The team held a party on the eve of the tournament.
on the eve of
Just prior to, as in On the eve of the conference the main speaker backed out. This expression uses eve, literally "the night before," more loosely. [Late 1700s]