Nedarim 8:1-2

Nedarim 8:1

If a person says “Konam that I taste wine today,” he is only prohibited until it gets dark. “…This week,” he is prohibited the rest of the week, Shabbos counting as the last day of the week. “…This month,” he is prohibited the rest of the month, Rosh Chodesh counting as the start of the next month. “…This year,” he is prohibited the rest of the year, Rosh Hashana counting as the start of the next year. “…This sabbatical cycle,” he is prohibited the rest of the cycle, the sabbatical year counting as the last year of the cycle. If he vowed not to taste wine for “one day,” “one week,” “one month,” “one year” or “one sabbatical cycle,” he is prohibited from day to day (i.e., for 24 hours, seven days, etc.).

Nedarim 8:2

If one vows not to taste wine “until Passover,” he may not have it before Passover (but he may have it on Passover). “…Until it will be Passover,” he is prohibited until Passover is over (because his words imply inclusion). If he says “until before Passover,” Rabbi Meir says he is only prohibited until Passover arrives but Rabbi Yosi says his vow lasts through Passover.