Mischna zu Wajikra 13:5

A bright spot in which there were no signs of uncleanness: At the beginning, or at the end of the first week, he is isolated; At the end of the second week or after it had been pronounced clean, he is pronounced clean. If while the priest was about to isolate him or to pronounce him clean, signs of uncleanness appeared in it, he certifies him as unclean. A bright spot in which there are signs of uncleanness, he certifies him as unclean. If while the priest was about to certify it as unclean the signs of uncleanness disappeared: If at the beginning, or at the end of the first week, he isolates him; But if at the end of the second week or after the spot had been pronounced clean, he is pronounced clean.