2,808. "This Month," "This Year"
Hilchos Nedarim 10:3
If one vows not to drink wine “this month,” he is prohibited for the rest of the month, though he is permitted to drink wine on the next Rosh Chodesh even if the month is deficient (i.e., 29 days long rather than 30). If one vows not to drink wine for a whole month, he is prohibited for 30 full days of 24 hours.* If he vows not to drink wine for “a month,” he is prohibited for 30 full days out of doubt.
Hilchos Nedarim 10:4
If someone vows not to eat meat “this year,” even if there’s just one day left in the year, he is only prohibited that day and he may eat meat on Rosh Hashana. This is because the start of the year vis-à-vis vows is the first day of Tishrei. If he vows not to eat meat for one year, he is prohibited for a full year of days; in a leap year, he also prohibited in the extra month. If he vows not to eat meat for “a year,” he is prohibited for a whole year of days out of doubt.
*i.e., if he vowed at 4:00 pm, the prohibition lasts until 4:00 pm on the last day.