Separating chalah from dough is the mitzvah, the obligation, of the woman. It is specifically her mitzvah, and she has priority to do it over her husband. In fact, there is a discussion among poskim whether she is considered her husbands shaliach, emissary, or if it is her mitzvah independently. Indeed, some poskim say that if a husband separates the chalah instead of his wife he owes her a payment of asarah zehuvim, the amount of money one owes another if they usurp anothers mitzvah. Others opine that he does not have to pay her since the dough belongs to the husband, as do all of a wifes earnings in lieu of his obligation to support her. The same applies if the husband lights the Shabbos or Yom Tov candles, which is the wifes mitzvah, before she has a chance to light them. The only time the husband may light the candles is if his wife is running so late that it is almost shkiah, sunset, after which lighting is no longer be permitted, or if she is unavailable to light them herself.