Question

Hello Rabbi,
When a good practice that is done 3 times turns into a vow, which of the following two possibilities is correct:
1. Upon doing the act the third time, a vow takes effect;
2. The third performance merely indicates that from the outset the person intended to do the act on a regular basis, and therefore there is a vow.
 
The question occurred to me regarding a woman who had the practice of hearing the reading of Parashat Zakhor, but wants to stop. If on the eve of Yom Kippur of the first and second year she said the declaration ("a vow that I may vow shall be void"), then apparently according to option 2 she can stop without annulment of vows. But according to option 1, if she did not say the declaration in the third year, then she would need annulment of vows.