Mischna zu Schemot 21:20

One who had [a discharge of] semen does not defile due to zivah for a period of twenty-four hours. Rabbi Yose says: [only] that day. A non-Jew who had a discharge of semen and then converted, he immediately becomes unclean due to zivah. [A woman] who had [an issue] of blood, or had experienced difficulty [in childbirth], [the time prescribed] is twenty-four hours. One who strikes his slave, the "day or two" is twenty-four hours. A dog that eats a corpse's flesh, for three days from one time of day to the same time of day, it is considered to be in its natural state.