Related for Rosh Hashanah 24:7
אפי' למאן דאמר יום אחד בשנה אינו חשוב שנה לצעוריה נפשיה קביל עליה והא אצטער ליה
[This means] a year in which there is only one tithe. How is one to act?
Tosefta Rosh Hashanah (Lieberman)
How [one should understand]: "for the vows"? [Answer:] If one has been forbidden by a vow to use another for a year, he counts twelve months from this specific day and onward. But if he says: For this year, even if he has denied himself the benefit of it by the vow only on the first in Elul, [the obligation] is only up to the first of Tishrei.
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