Vows for a good deed

Hello Rabbi,
When a good deed done 3 times becomes a vow, which of the two options is correct:
1. Upon performing the act for the third time, a vow is created;
2. The act in the third act only indicates that from the beginning the person intended to do the act regularly, and therefore there is a vow.
 
The question occurred to me regarding a woman who used to hear Parashat Zachor, but wants to stop. If on the eve of Yom Kippur of the first and second years she said the announcement ("The vow that I will make to be a priest shall be null"), then apparently according to option B she can stop without breaking her vows. But according to option A, if she did not say the announcement in the third year, then she must break her vows.