A husband can annul his wife's vows that she makes, for a single calendar day after he hears it. This means that if he hears it at night, he has nearly 24 hours until the next sunset; in the morning, only around 12 until sunset, and very little time in the evening. (Rambam Hilchot Nedarim 12:15)
Let's say that it is an hour until sunset, and the husband is quite busy. Someone comes and tells him, "your wife made a vow." Can the husband then say, "don't tell me what it is until after sunset, so that i have another day to decide"?
In other words, does the clock start from when he hears that the vow exists, or is it from when he hears the content of the vow?