on the eve of

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.
See also: of, on

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]
See also: of, on