Niddah 1:2

Her time is sufficient, as follows: If a woman was sitting on her bed and busy handling ritually-pure objects, then she got up and saw blood, she is ritually unclean but those objects remain ritually clean. Even though the Sages said that a woman is ritual impurity retroactive for 24 hours, a woman with a fixed cycle only counts her impurity from the time she saw blood.

Niddah 1:3

Rabbi Eliezer says that there are four women for whom their time is sufficient: a “virgin,” a pregnant woman, a nursing woman and an “old” woman. Rabbi Yehoshua says that he only heard this law regarding a “virgin.” Nevertheless the law follows Rabbi Eliezer.